Am I being over sensitive?

[MKAW222]

Today, my 10 year old son and his friend had to miss the end of their PE lesson because they had kicked a rugby ball after being asked not to. They were sent to another teacher. Another child asked why they had been sent there and the teacher, in front of them, said, "Some people don't have brains". My son suffers from anxiety and low self esteem and is receiving counselling through CAMHS. He is awaiting diagnosis of ASD. This has really upset and humiliated him. Should I let it go or make a complaint? I am so sad for him.

For goodness sake! What is wrong with people nowadays; having to analyse every sentence?

As an adult with authority, you don't tell a child that another child has no brains! It's really not that hard to understand. The comment was insulting and unnecessary. The adult should have engaged their own brain and used different language when discussing one child with another.
OP has said many times the poor behaviour has been addressed. Children are naughty sometimes. Adults, however should know better.