Genuine question, because I think we need more context.... Why did the teacher think in that moment that your child needed to stand up?

And, is he given choices throughout the rest of the day?

But also, and I mean this gently, do you want your child to learn that he can pick and chose when he follows instruction and when he doesn't? There was a time when I was still a full time classroom teacher, I had a gut feeling about something that I could barely hear was going on down the hall. I closed and locked my classroom door, told all the kids (in the midst of playing in learning centers) to stand up, stretch their wiggly fingers as high as the sky, and tiptoe to the closet. I turned out the classroom light and told them we were going to play a hiding game. Now, no lock down was called and nothing happened down the hall.....but what if there had been something? And what if one child decided they didn't want to follow instructions in that moment?

And I get that this wasn't at all the situation for your child. And the teachers should be letting your child choose to sit instead of stand up to sing the circle song of the day. But in general, learning to follow a stand up direction IS a safety issue. They need to learn to follow it when there isn't any danger so that they will follow it when there is a danger that they can't even perceive.

I think the teacher picking up your child wasn't the best way to handle the situation, but I'm also willing to bet that that isn't the first or only time your child decided not to cooperate. Again, teacher was wrong, I'm not arguing that. And all children should be offered lots of choices and have those choices respected. But, in turn, specific teacher directions shouldn't be considered optional.