I'm trying to decide if he'll know what she is. The only supernatural creatures he's come across in canon are angels and a demon, and the demon's a friend of his and the angels are all his siblings, so he knows them. He knows that humans are humans because they're not his siblings. But I assume that since they're not human, they have a different "feel" than humans do and he'll be able to figure it out eventually. Just be confused for a bit because she is not one of the supernatural beings he knows.