He was almost killed and witnessed the atrocities committed by his fellow classmates, it also wasn't confirmed if she actually was raped by the group who attacked her. MC may have saved her before that happened. Even so it's not like the two of them have wildly different reasons for not wanting to trust other humans.
They both went through hell, they both have a right to be wary of each other and other humans.
The illustrations were clear enough, she was raped. What bothers me about the MC is that he literally learned his lesson 2 chapters ago, and knows she's as much a victim as he is, and is close to someone with the memories of a human, and progress on his ability to trust her was shown two chapters ago.
It's one thing to have a trauma, it's another thing entirely to have the story revert the progress the MC was making for no good reason. It's disproportionate to what the story has already shown us, and is thus artificial drama. It's just a bit of bad writing, plain and simple.
Is it enough to completely throw away the story? No. But it does irritate me to see published authors get away with unprofessional writing. At this rate, by the time my book is finished, it'll be considered university-level writing in comparison to future published writing.