Well I am sure he probably is interested in you but asking for your number doesn't necessarily mean he does.
As example when I went to Post-Secondary School the guys in the hall I was in all had a competition for getting the most girls numbers. So they all went off to get them. I, on the other hand didn't really stress out about it all and go crazy like they did. I just asked girls for their numbers in case I miss class or if I need someone to study with and the same goes for her sort of deal. Well I completely destroyed my opponents. I highly doubt it is something like this in your case but it was just merely a story I wished to share.