As far as the principal questioning him, it was poor judgement on her part not to have a witness to protect her.
It sounds like she followed what I would consider reasonable steps in that she questioned the boys separately, took notes, asked the boys to reflect on their decision and connect this experience with another case of poor judgement. Then, as far as punishment goes, she left it up to you the parent. All she wants, from what I can tell, is your acknowledgement of the situation. Missing recess is only if he doesn't return the note. The punishment comes only if he doesn't let his parents know.
However, you seem to be very upset by this and I'm wondering if there is something else that happened that I'm not picking up on.
I couldn't agree more. Parent needs to put this in proper perspective.
Good parsing!