Erections can be "contagious". That's a place where you're nude, you're in front of other nude guys so of course Murphy's Law you'll get one, especially if one guy already got one and "broke the ice". If you watch this video, these guys aren't "looking at each other" or making ANY kind of attempts to touch one another.
I know what you mean. Yes they can, any there's nothing 'gay' about it.
Guys in public shower with hard on