Ignis doesn't come to the Coven for himself so much as he comes to simply learn about the world he's in. He's not the kind of person to keep himself isolated from the workings of the place even if he can't use the same talents that witches can.

He does attend lectures and sits in on classes occasionally, purely out of curiosity on his part. Also might be found in the library digging up every kind of reference he can find on the Cwyld.

As a Naga he has some measure of control over water, but I don't think there's a witch magical 'school' that really aligns to that? Do correct me if I'm wrong! No way of mistaking him for a witch as he's almost all the way changed (getting the tail this month aayyyy).