Even then it doesn't happen that often. Null did a bit in a stream about this.
Imagine citing null as a source for your life information lmao. It absolutely happens frequently, the thing is it's underreported and miscategorized. Males are incredibly unlikely to report being raped. Doesn't matter how severe, traumatizing, or motivation behind it, that itself is rare.
At of the rape is done from the guards. No one is going to report a guard. Thus these rapes don't happen. Now you have the large quantity of people agreeing to the rape ("but that's not...") stfu. First timers come in, find food on their bed, or their offered something, but wait I have to pay for this? It's been a week? I don't even have access to anything yet. Not reported.
Or they get their new cell, multiple people pop up to "rape them"/stomp the shit out of them, a savior swoops in an intervenes. "That was a close one. You're safe though, hang with me I'll protect you".... not reported.
So, yes, it does happen frequently. And it happens a lot in juvenile. It happens less that prison media portrays, but a lot more than you think. You're also ignoring the things that VASTLY increase the chances, all of which Chris has. He's white, he's not in shape/have any way to fight back, he's retarded, he "looks" feminine (lol) and says he's a woman (not gay!)
You're telling me if some large man offers Chris three chocolate bars and to come live in his cell because he has transformers, Chris won't go? Unless this is the only prison without any sort of sexual assault, or he's solitary, I would bet a lot of shit that Chris is absolutely going to have a sexually unpleasant time.