It is because they cite a specific verse from garuDa purANa which says maNiman demon reincarnated in kali yuga.
As per them the incarnation of vaayu in dwapara yuga was Bheem sena and the incarnation in kali yuga is Madwa (Ananda teertha) who came to defeat the demon maniman in kaliyuga who was previously destroyed in dwapara by bheem sena.
The views given below are for Sankara, his lineage, his philosophy as well as his disciples like padmapAda.
Kali and other demons (the enemies of Devatas) were very happy to hear
the plan of Dvpara (formerely Sakuni) and honoured Maniman with zeal
and spoke to him thus.
'O brother, salutations to you; take birth on earth and destroy the
Vedas, puranas and other scriptures completely soon'.
Being inspired or ordered in this way by Kali, Dvapara and other
demons, Maniman made up his mind to be born on earth although he had
fear of Bhimasena.
When the mind is spoiled, some people will be fickle minded and they
will readily accept our Mithyavada philosophy; those not influenced by
us, will neglect it; and only some people will try to refute the
After studying the Vedas, he went on a journey in the northern
direction and while he was crossing the river, he (Sankara) lost his sacred
thread - Yajnopavita - but he continued his journey.
Sankara said - 'O, Sacred cord, you are leaving me; note that I have
forsaken you earlier; of what use are you to me; who does not perform
Vedic karmas (actions)' So saying, he went away quickly.
The highly learned sage, Paratirtha observed the demonic signs on the
bachelor without sutra (sacred cord) and bent his head in disgust, and
went away after sipping water thrice as penance for having seen such a
Sankara made out that the sage was aware of the demonic features in
him, and hence he went to Badari after crossing river Godavari (Vrdha
Ganga). There, he met a disciple of Paratirtha, by name Satyaprajnya)
and told as follows:
'I am the disciple of your master (Paratirtha) and I have come here on
his permission', but he did not trust his words.
Satyaprajna found out at once that the bachelor was vile, devoid of
all good qualities like devotion, detachment from worldly passions and
in utter disgust, he abandoned him.
Having experience in his previous birth (as Maniman) and due to strong
memory in this birth, Sankara meditated on Brahman as attributeless
and with identity of souls (which amounts to Sunya tattva of
Once, the demons (Dvapara and others) approached him during a night
and respected him and said 'Sankaracharya, you are our solace'.
'O pure minded padatalotyaja (ie. A person born in Kaladi village) we
wish you happiness and prosperity. We think of you in full confidence,
as our agent in our task of destroying the Vedas'.
'We will enter the minds of the astikas (who have belief in Veda in
form and make them helpful to you and love you. You start
assassination the character of Vishnu by citing Vedas of wrong
interpretation). So saying the demons went away. (Thus the teachings
of Asuras from Stanza 24 to 39).
Govinda Bhatta readily accepted him as his disciple. Sankara told him
'We shall preach Sunyavada (Buddhism) in the guise of Vedanta or
otherwise, the people will abuse us as Non Vaidikas. As such, I will
study Brahmasutras under Brahmadatta (a sannyasi) to know the meaning
and significance of the same'.
The deceitful Sankara spread Buddhism only in the garb of
Brahmasutras; he substituted the words 'Sunya' and 'Samvriti' (of
Buddhism) respectively by words 'Brahma' and 'avidya' (of Vedanta),
the characteristics being the same.
Five wicked persons by name Totaka, Padmapada, Jnanothama, Bijada
became disciples of the deceit Sankara.
Notes: They were wicked because they destroyed the minds of even the
saintly persons by their perverted teachings.
When his death was approaching, Sankara was suffering from veneral
diseases, fever and deep breath. His voice became very feeble.
The deceitful disciples, who were the enemies of Vedas, went to their
dying master hastily and asked 'revered master, what we have to do
Sankara told them 'O Great Demons, I have almost done my duty; but the
disciples of the Great Paratirtha have to be destroyed.'
So saying to the Great Demons, who were capable of executing the
instructions, Sankara called four other intelligent demons and told
'You go to Beejada and ask him what are the difficulties and sorrows I
have to face in my future births'. They went in all the ten directions
and came back to him.