I have a gay friend who would most likely have agreed with your friend. He hates it when anybody makes out in public, no matter their sex, the only exception is probably at a bar or club where acting out is usually accepted.
It's kind of like when I got in a fight with a black guy, I got pinned by some people as being racist, but not him... noooo, he was just figting to protect himself. People are so quick to throw the race card or the homophobia card or the sexist card, it frankly disgusts me. Usually if I give you a hard time or something it most likely has nothing to do with the fact you ahve a different skin color, have a vagina, or like to kiss other men....it's probably because you are an asshole and I don't like you as a person in general.
So no, you guys were not in the wrong. The fact that they were gay should have not been the issue. Ans spittting on someone is technically assault.