I would say after this I am out of this thread..but probably not.
OP, how do you know for SURE what was said between teacher and child when they had their conversation. You say your son is shy and has anxiety. That type of child has great difficulty having those conversations with an adult, especially one in authority like a teacher. Your ds may have felt that somehow he conveyed to the teacher he did not want the grade displayed or that he was embarrassed. However, possibly that's not how it came across to the teacher. Maybe he said he was worried about his parents seeing his project, maybe there was something that made her think he was nervous about something, not necessarily that grade being displayed. He thought he said the right things?
OP, you are right that since you know all the story you have a better handle on things and what you did you can be o.k. with. You haven't really conveyed any details that shed light on ALL of the sides in the story. So we are left to make assumptions in reply.
Kelly