I'll have to investigate more, but I don't think the daydreaming is taking up a huge portion of the day. I think he's generally OK with school, and the school continues to work to create appropriate programming. That said, I will guess that there are still plenty of opportunities to daydream.
I agree with you - if he were clearly happy that he wasn't being challenged, that would worry me. I'm glad that he's sharing that he's bored and would prefer more challenging work. The alternative - happy to be coasting -- would be much worse.