From what I can see, the hypothesis links Cernunnos serpent iconography generally and this figure particularly with the concluding passage of the Táin Bó Fraích
Fúabbrait in less. Focheirdd ind nathir bedg i criss Conaill Chernaig, 7 orgait in dún fo chétóir. Tessairgit íarum in mnai 7 na trí maccu, 7 doberat a n-as dech sét in dúine, 7 léicid Conall in nathir assa chriss, 7 ní dergéni nechtar de olc fria chéile.
- Táin Bó Fraích
"We will go truly," says Conall. They attack the Liss; the serpent darts leap into the girdle of Conall Cernach, and they plunder the dun at once. They save off then the woman and the three sons, and they carry away whatever was the best of the gems of the dun, and Conall lets the serpent out of his girdle, and neither of them did harm to the other.
The passage is strange but I don't know how much one can read into it. It's not Its worth remembering that the text of Táin Bó Fraích is itself fragmentary and reconstructed from five or six manuscript sources. So it certainly is a bit of a bizarre interlude, but it may be missing lost context.