I have I say in this case I have no concern with the questions being asked in front of the child - it was not their class room teacher, the child felt unjustly accused, and the teacher behaved rudely. Surely we should be teaching our kids that it's not ok to be rude, and that we will investigate if they feel unfairly treated? We, as parents and school council members, have questioned several proposed and current policies, and the staff have only ever been understanding and happy to listen - and honestly having seen the way some policies have been barely considered and pushed through, I think it's great to have people who are willing to question them.
As far as parents being reasonable for teaching boundaries etc, of course we are! But given that the majority of a child's social contact with peers happens at school, there must be some place for learning this stuff too? If a child spends majority of his days at school, with a hands off policy, for 12 years, how likely is he to have learned clearly what is and isn't appropriate?