It doesn't really matter if he was making a statement or being a lazy shit. He's free to do either. We can say "just stand, it's no big deal" but that is exactly how we end up with an ever-encroaching government. It's a way to slowly chip away at freedoms, all because it is incremental.
The teacher doesn't need to be made aware, since the kid is not required to take part. If it's for religious reasons, great. If it's not, also great. Honestly, it's none of the teacher's business.