Exactly. We're to believe that he can't think properly, but that he's also capable of not only reading the novel, but also using the plot of that novel to describe what happened to the victim in an attempt to have the cops questioning him let him return to class. Pretty diabolical for a dum-dum. I believe his story of Steven forcing him to help kill and destroy evidence, but I also despise the interrogation techniques used to get him to admit it all. The most convincing testimony he gave was in the calls to his mother that he didn't know were being recorded.
I dunno... in the one private phone convo with his mom, he doesn't know what the word "inconsistent" means. I think it's possible he heard of the book or movie and just had a general sense of what it was about. Or possibly someone fed him the line that he should say that's how he came up with everything.