According to Baladeva Vidyabhusana as he explained in Govinda Bhasya commentary on Brahma Sutra 'I am Gopala'(as said in GOpala Tapani Upanishad), is an ecstatic symptom of love of God. Therefore 'I am Brahman' is an expression of ecstatic symptom of love of God.
But, there are other interpretations also..
First, according to Gaudiya Vaishnavism, Bhagavatam makes it clear in the beginning what it is going to teach and it is not absolute non dualism. Jiva goswamis explains it in tattva sandarbha.
Since some user already wrote an explanation of that here https://hinduism.stackexchange.com/a/31853/2612. one may just refer that why they think so.
Coming to the verse you said,
Here is how Vishwanth Chakravarty interprets in sarartha darshini, this verse has dual meanings.
First meaning is:
“I am that Brahman, the supreme state of being. Brahman is I, the
supreme position.” Considering this, place yourself in the Brahman
devoid of upadhis. You will not see Taksaka biting your foot with fire
and poison and licking it with his tongue. You will not see your body
or the universe to be separate from Brahman.
The esoteric meaning is:
I am the worshiper of the Lord. I am a conscious particle of the Lord.
I belong to the Lord.” Considering this and considering the lotus feet
of the Lord surrender to the Lord. You will not see Taksaka, your
body or the universe separate from the Lord because of fainting with
bliss on seeing Krsna.
The commentary is as follows:
For the first translation:
In two verses the method of deliberation and the bite of Takska are
described. By thinking “I am that Brahman, not a person in samsara”
one can eliminate lamentation. By thinking “Brahman is I, I am
Brahman” one can eliminate the invisibility of Brahman (one can attain
realization of Brahman). You should place yourself in the Brahman
(atmani) free of upadhis (niskale).
For second translation:
The esoteric meaning is “I am the spiritual particle (dhama) of the
Supreme Lord who is like the sun.” Amara-kosa says dhama means body,
house, splendor and beauty. I am the worshipper of Brahman
(brahma-param). An example of para with this meaning is narayanaparo
viprah: the brahmana is a worshipper of Narayana. Brahma aham means “I
belong to the Supreme Lord.” This is tat-purusa compound with a
possessive meaning. Seeing the lotus feet of the Lord or his svarupa
(paramam padam), you should surrender yourself to Paramatma, Krsna,
who has a niska * (Niska is a gold ornament worn on the chest.)
ornament on his chest (niskale). You will not see Taksaka, who bites
while pressing his two lips and relishing with his tongue, using fire
combined with poison. You will not see your body bitten by the snake
or the universe to be different from Brahman. The other meaning is
“You will not see all this because you will be fainting with bliss
from directly seeing the lotus feet of Krsna.”
According to Vishwanath Chakravarty, Bhagavatam speaks with double meanings to attract different types of audience. He compares it to the nature of Mohini avatar. Mohini says one thing and does another thing.
This is what Vishwanath Chakravarty says in another similar verse 12.13.11-12:
sarva-vedanta-saram yad brahmatmaikatva-laksanam
vastv advitiyam tan-nistham kaivalyaika-prayojanam|| SB 12.13.11-12 ||
From beginning to end, the Srimad-Bhagavatam is full of the Lord’s
pastimes which give bliss to devotees endowed with a sense of
renunciation. This Bhagavatam is the essence of all Vedanta philosophy
because its subject matter is one Brahman, a substance with no
duality. The main goal of the work is merging.
The esoteric meanings is:
From beginning to end, the Śrīmad-Bhāgavatam is full of narrations
that encourage renunciation of material life, as well as nectarean
accounts of Lord Hari’s transcendental pastimes, which give ecstasy to
the saintly devotees and demigods. This Bhāgavatam is the essence of
all Vedānta philosophy because its subject matter is the Absolute
Truth, which, while nondifferent from the spirit soul, is the ultimate
reality, one without a second. The goal of this literature is
exclusive devotional service unto that Supreme Truth.
He comments as follows:
This verse speaks of the subject matter and goal. The host (vrata) of topics
concerning the pastimes of the Lord is sweet. The devotees who are called
devatas become blissful because of these topics. The subject of these topics is
bhakti, and bhakti is sweet nectar. The goal is prema, because by prema one can
taste the sweetness of bhakti-rasa. The phrase “it gives bliss to the devotees”
means that the devotee’s experience of prema. By the use of the words nectar
and devatas, the Bhagavatam giving nectar to the devotees is indicated. By this,
the scripture’s nature as Mohini is indicated, since she is famous for giving
nectar to the devatas. With a movement of her brow to the devotees who know
her identity, unseen by others, she says “Appearing in this way, I must be
favorable to you. Cheating the demons, I will give you nectar.”
By moving her eyebrows at the demons who do not know her identity, she says
clearly, “By my appearance you should gain victory. Giving you nectar is a
secondary affair. The main thing is that I will constantly give you astonishing
bliss while you remain householders. I will serve a little nectar first to the lowly
devatas. ” Similarly the Bhagavatam in half a verse, speaking of the giving the
devotees nectar of his pastimes, indicates the goal of the Bhagavatam. But the
Lord has also said paroksa-vada rsayah paroksam mama ca priyam: the Vedic
seers and mantras deal in esoteric terms, and I also am pleased by such
confidential descriptions. (SB 11.21.35) Thus having said what is unnoticed by
most people, he speaks another subject and goal for the person who does not
know the Lord but thinks he knows scriptures. “It is the essence of all Vedantas,
which is oneness with Brahman, an object with no duality. The work has
Brahman as its subject (nistham) and merging in Brahman as its main goal.”
Some people explain the verse as follows. Because this scripture speaks of both
bhakti and jnana, after speaking of the subject and goal of bhakti and prema, the
work then speaks of jnana and merging as the subject and goal. Brahman is the
subject. This work has as its goal merging (kaivalyam) as its one goal.
Others explain as follows. At the beginning of this work it is understood from
the second verse that bhakti is the subject with the words (dharmah projjhitakaitavo
‘tra) and from the same verse with the words sadyo hrdy avarudhyate
atra krtibhih it is understood the prema is the goal. Thus by the predominance of
bhakti over jnana and liberation, its goal, in the whole work, bhakti is indicated
as the main subject and prema is the goal.
It is also necessary to give an esoteric meaning to the verse so it becomes
suitable for devotees, in the manner of Mohini’s appearance to both parties. The
meaning tan-nistham is as follows. This work remains (stham), having given up
(nisrtya) Brahman and merging. The work has as its goal only the mood of
exclusive devotion (kaivalyam), devoid of jnana, karma and Svarga.