As far as my understanding, it's talking about the contradictory nature of Brahman which is beyond the grasp of anyone or anything. It is Nirguna but still is Saguna and neti-neti.
Maitreya Upanishad in its Tritiya Adhyaya (Chapter 3) gives totally contradictory nature of Brahman. Of which I am giving some verses.:
III-4. I am devoid of honour and dishonour, I am without attributes (nirguna), I am Shiva, I am free from duality (dvaita) and non-duality (advaita), I am free from the pairs (of opposites), I am He.
III-5. I am devoid of being and non-being, I am beyond speech, I am effulgence, I am the power of the void (zero) and the non-void (non-zero) and I am the auspicious and the inauspicious (i.e. beyond both of them).
III-7. I am beyond the number one and I am beyond the number two as well. I am above the distinction of good and bad and I am devoid of ideation.
III-19. I am free of space and time, I am the bliss of the principal unclad sages, I am beyond ‘there is’ and ‘there is not’ and I am devoid of all negation (i.e. I am pure Existence without a counterpart).
III-22. I am above the body and its dweller and I am unique, *devoid of attributes (nirguna). I am beyond liberation, I am liberated and I am always devoid of final emancipation.
There are almost 25 such contradictory verses.
As you can see here Brahman is said beyond dvaita, advaita, void, non-void, single, double, etc etc...
There can also be another logic.:
The 5 states.:
Mandala Brahmana Upanishad.:
2.4. There are five Avasthas (states): Jagrat (waking), Swapna (dreaming), Sushupti (dreamless sleeping), the Turya (fourth) and Turyatita (that beyond the fourth).
The 1st 3 states comes under duality where as the 4th comes under non-duality.
Mandukya Upanishad.:
In which all phenomena come to a cessation, and which is unchanging fourth (Turiya), peaceful (Shanta), auspicious Shiva, and non-dual. That is the Self; that is to be known. 7.
Parambraha Upanishad.:
There is nothing other than Brahman of the five padas (i.e. the turyatita)... 5.
Srimad Devi Bhagwatam 12.8.:
O King! Hearing this, the Umā Parvatī Maheśvarī Bhagavatī replied to Indra.,
62-83. ". . Brahmā, Viṣṇu and Maheśa are of the nature of the three guṇas. Brahmā has the Rājo guṇa in Him preponderating; in Viṣṇu, the Sāttva guṇa preponderates and in Maheśa, the Cause of all Causes, is said to reside the Tāmo guṇa. Brahmā is known as of the Gross Body; Viṣṇu is known as of the Subtle Body; and Rudra is known as of the Causal Body and I am known as Turīya, transcending the Guṇas.
This Turīya Form of Mine is called the state of equilibrium of the Guṇas. It is the Inner Controller of all. Beyond (Atīta) this there is another state of Mine which is called the Formless Brahmā (Brāhmaṇ having no Forms). Know, verily, that my Forms are two, as they are with or without attributes (Saguṇa or Nirguṇa). That which is beyond Māyā and the Māyic qualities is called Nirguṇa (without Prākritic attributes) and that which is within Māyā is called Saguṇa. . ."
Again,
Sri Shiva Purana 2.1:1:8.:
4-5. “What shall be this great sound?” thinking like this I stood perplexed. Viṣṇu who is worthy of respect from all the Gods, who is free from all inimical thoughts, saw with the delightful heart, the eternal being’s manifestation on the right side of the liṅga. First, he saw the syllable “A” and he saw the syllable “U” thereafter.
6-10. He saw the syllable “M” in the middle and Nāda (the mystical sound) in the form “Oṃ” in the end. He saw the first syllable on the right like the blazing sphere of the sun. O foremost of sages, thereafter he saw the syllable “U” dazzling like fire. In the middle he saw the syllable “M” glittering like the lunar sphere. Above that what he saw was the supreme Brahman, the greatest refuge. It had the lustre of the pure crystal. It was the pure Being beyond (atita) the Fourth (Turīya), the unsullied & free from extraneous harassment. It was free from mutually clashing opposites. It was single (isolated), void, free from exterior and interior though stationed in the exterior and the interior, devoid of beginning, middle and end, the primordial cause of Bliss, the truth, The Bliss and the Nectar.
Even Guru Dattatreya also says the same.
Avadhoota Gita of Sri Dattatreya 1.62.:
62 ) The world of form and the formless Void : Neither of these exists independently . In the One , there is neither separation nor union ; All is called no-no (not this-not that/neti-neti). Truly , there is nothing but Shiva alone freed from all these differences.
I hope this helps. Prd..