Unsourced, but I'd guess you're right. Which probably has more to do with the fact that there are statistically many more straight men than gay men, of course. Realistically, the amount of gay men raping other men in the bathroom is very, very low. Even taking into account the fact that most people are straight, you'll find bathroom rapes are very uncommon.
But most Guy/guy rapes are prison rape and/or Pedophilia.
More unsourced nonsense.