@Bubbles85,
I don't know the guy therefore, I'm not able to make a judgment as to his sexual preference. However, what I can tell you is that some people are confused with being gay when they aren't. Just yesterday a friend of mines (girl) comes out of nowhere and tells me "what, you not gay?" to which I reply "no". The question totally caught me by surprise and totally killed the mood. Here I am being nice to this girl which I find cute and have many things in common and she comes up with that out of nowhere.
Overall my point is, some people might be seen by others as gay yet are completely straight. In my case, I'm 100% straight, the idea of being with another dude has never even once crossed my mind and is repulsive (no offense to any gay people, but it just isn't my thing). Now in your friends case, if you caught the guy with other dudes making out ect. then things are odd...