He is an actual lion! Uh and also sort of humanized in that he doesn't have a tail.

He comes from a canon where lions can look like lions, but they can also look like human-lion hybrids. In fact, his sister's and his mother looks like normal lionesses, he once fought another lion with a lion's head and a human body and Lion looks...pretty much like what he does now except without a tail.

Also he would not understand how you can be a lion in a human skin...or what a human is for that matter. XD;;