Talk:Demon/@comment-62.158.66.136-20180804171820/@comment-67.86.43.170-20181225024558

He never denied being a Demon: when Geralt asks, Gaunter simply dances around the question by saying if he told him his true nature, he would die, and he needs him alive.

As the saying goes, if it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck. He fits the bill of an exceptionally powerful Demon, and the Cat/Dog Demons clearly know about him.