I feel sympathy for Joel. Throughout his life in middle school, he has been bullied, and it was basically considered as the norm for him. He got bullied to the point he had to go to boarding school which he didn't like. When he hears the news that his main bully, Chase, has changed into a better person, he still distastes him.
If I were in his situation, I'd feel the exact same. Imagine the very person who bullies you to the point you had to move schools is suddenly acting all nice to you. I would feel very skeptical and uncertain.