Based on your earlier posts, I am wondering if it is possible that the "I don't like school" comments are an attempt to get you or your husband to homeschool him?
You might try questions such as "what would make school a place you'd like? How would you change it to fit you better? What would a great school day be like for you?"
If he's an introvert and doesn't seem unhappy about the playground situation, that's probably not the issue. (There's an example almost identical to the one you describe in Susan Cain's book, "Quiet.")
