He probably just thinks you look attractive then. People don't have to be attracted to a specific gender to find someone attractive. Like there's a study I read a while ago about how straight women check other women out too. Doesn't really mean anything. People just like to look at things they find aesthetically pleasing.
He could be checking out your outfit, lots of gay guys are into fashion and that kind of thing. Also, you can appreciate someone's looks even if you're not attracted to the gender they belong to. They can still be eye candy.