NP and I've read through all the posts and I don't think anyone is downplaying the seriousness of the behavior on either side of the wording discussion and to suggest otherwise seems pretty ignorant or that you have some sort of agenda here. Agree with PP that this is not helpful to OP.
I wanted to suggest to OP that CBT may be helpful to her child so that he can begin to understand himself why he's behaving this way. He's smart and in 3rd and that's old enough to start self reflecting.
I'm not the person you're responding to but I agree with her. I'm not sure why this has touched such a nerve with you and I don't know why you are so invested in controlling the discussion. It appears the two sides to this discussion are those who are downplaying the seriousness of the behavior by calling it merely 'aggressive' and explaining it as 'sensory issues' or 'he was terrified' or 'context'. There are others (me included) who are believe it is more serious because, from OP's posts, these behaviors occur across environments, are not new and she sometimes thinks he does it to be mean. The hard pinch he gave to his sibling is atypical behavior for a third grader. This child needs interventions and not just a change in environment or teacher. OP is right to be concerned and actively seeking
assistance.
He isn't violent most of the time but sometimes I do think he does some actions to be mean when he doesn't get his way. For example, tonight, his little brother was talking and he wanted him to stop so he pinched him hard. Right in front of his father.