I think it depends on where this restroom is and who you're in there with. A total stranger who happened to enter at the same time or maybe was there first might not expect (or want) another guy too close while pissing. But if you're with friends, gay or straight, walking too far away is wierd in itself, especially if you're having a conversation about the movie you just watched.
Now in a bar, there's usually only 1 or 2 pissers and maybe 1 toilet in the whole restroom, so you go and do what you have to, nevermind who's there. But in a bar or club, everyone's usually drinking and feeling good, so even the prudes can chill out enough to piss next to the gay man with the big dick.
Always consider the context. All in all, I think you handled the situation well.