Sceptical. They were pretty monitored, heart rate etc. Plus three military hard cases, not two. Even taking 10%, the odds are just very very long.
Not that long, actually. Given P(gay) = 0.1 and assuming astronaut screening does not bias this, the probability of two astronauts in a three-man capsule being gay is 3 * 0.9 * 0.1 * 0.1 = 0.027. But as you say, they're closely monitored, not the least by the presumptive odd-man-out, who might object to the shenanigans.
These guys had strong egos, but they were selected in part for their ability to get along with each other for two weeks in a small capsule. So, no matter what their orientation, I can imagine that they could put it aside for the duration of the mission.
And while we're on the subject of gay astronauts, let's give a nod to American space pioneer Sally Ride. May she rest in peace.