Hm, if one experiences pure physical sexual attraction, it would make him/her superficial?
From Google, the definition of superficial, the part that applies here.
Concerned with or comprehending only what is apparent or obvious; shallow.
It is not apparent or obvious, so he's not superficial. He's going out with her for crying out loud. And liked her before hand, now he's more attracted to her. He's not only concerned with her looks or the obvious of her (because he only caught on to this feeling now).