Totally agree with TPM - you don't have a fastball then it's going to be very hard to do well in the game. If you're facing a top team like you said he was then if he can't get the fastball by them then the changeup won't be much better. He might fool them once but if they don't have to worry about being late on a fastball they can sit on a change.
Maybe you're right and the coach isn't very good but this is just one start. I wouldn't panic or start questioning things after one start because he's got a long HS career ahead of him. Probably won't enjoy it that much if start questioning everything.