A bad decision by the teacher I feel.
Teachers are acting 'in loco parentis'.
If one of my children had come home from school and showed me the video I'd be seriously concerned.
He may well have raised a few giggles and grabbed the pupils' attention but it was undignified and not an example of a good role model in my opinion. He's their TEACHER not their friend.
But I bet none of the pupils will forget that lesson