My comments about stereotypes being sometimes accurate can best be explained by a statement Chris Rock made recently during one of his comic performances, "If you want to hide money from a black thief, hide it in a book. Books are like Kryptonite to a black person."
You misheard Chris Rock. He did not say what you quoted. In the joke you're referring to, he was discussing the difference between a black person and a ni**er. He said books are like Kryptonite to a ni**er, not to a black person. Though I deplore the use of that word, he was using it in the joke to make his point that blacks and ni**ers are NOT one and the same.
Just pointing it out.