I wouldn't actually be surprised if his IQ is above average, at least on paper. I think he is a tard by choice, and that his parents basically amplified his autism to the point of turning him into a tard by completely refusing anything other than mainstreaming him. If the tale about Bob basically paying girls to be his friends is true, they were also his worst trolls, because his formative years where you learn how to interact with the opposite sex were warped because every interaction in his life was staged or influenced by others.
Already autistic, he was doubly fucked because most of his interactions with other people even before Internet trolls were essentially fake. He didn't really have any models for proper behavior because his parents deliberately deprived him of them. They didn't intend to harm him by doing this, but they certainly didn't understand autism or how to raise an autistic child, and did exactly the opposite of what any sane people would have done.
tl;dr the irl version of The Truman Show is more like Cronenberg's version of The Fly. Chris's personality is a deformed mess.