Thanks for all the feedback. I too felt it was way too harsh. The teacher was at the performance and watched him perform, so she definitely could understand the reason he was tired.
She is a very young teacher with no kids or her own who hasn't much experience with younger grades. I am letting it go. We have had much bigger problems that I have addressed a bit with the administration and some emailing with the teacher. Ready to move on and hope for a much better year next year!