Been there, though my DD didn't look entirely happy, she hid it with compliance and a depression which they mistook for shyness. My DD is not shy, so that's a behavioral red flag for her.
I find in my advocacy efforts that it's best to ignore any conversations about happiness and focus on learning. If the school brings it up, I'd say, "That's great, but he doesn't come to school to be happy. He comes here to learn." Anytime they stray, I always redirect to that. I even put a statement to the effect of "DD needs to be learning" in her GIEP this year.
It's inevitable that they'll start with the "think about the entire child" line, with reference to socializing, sports, etc. Again, that can be easily redirected towards the core subject... "I am thinking about the entire child. I'm deeply worried about how his attitudes towards learning and coping with challenges will be affected if he spends an entire year in school not learning."
