discipline? yes. punish? no.
I agree. I don't see the problem with others teaching my child social norms and considerate behaviour. I send my son to preschool so I expect him to be taught by others.

But some of the examples such as time out etc are punishments and I don't believe in adult directed "consequences" so I would not be happy for someone else to do that to my child.

I comfortably comment on other children's behaviour if I feel it's needed, such as "He had that toy, I can see another one over there you can have" if I see a child snatch something off another child and upset them and I'm more than happy for others to do the same with my children.