If his arguement is largely just that he dose not see you as a woman because your both hanging out like always it is likely his perception. I am going to assume he is heterosexual and that most of his past history hanging out with women either he had an attraction to them that makes it feel very diffrent, he did not have much in common with them or they where naturally reserved around him as most women are around men they do not know very well.
the fact that he is not attracted to you, the fact that your comfortable talking to him like you always have and you have common hobbies and history together makes it feel like his relationships with his male friends. He may like many men have trouble thinking of women as people, not in a awful way but in the sense that growing up they where always the other the ones you saw but never interacted with, there interests, hobbies, likes, and dislikes strange and unknowable. To be shown that women can and do act just like him brushes up against his past that tells him women are not like that and you can't possibly be a woman because he understands and relates to the things you like.
Or I am overly tired and reading way to far into this and he just needs time to proccess and get to know the new you.
Serena