There was an incident in DD's class yesterday, the art teacher left the class for a moment to fetch something from another classroom. During that time, one boy (call him boy A) hit another boy (boy B) very hard. Boy B ran out of the classroom crying and boy A stormed out just as the teacher was returning. The teacher asked the rest of the class what had happened, now both boys were gone, and then said to the class that they must not annoy boy A because he reacts easily like this.
She hadn't been told if there was any argument or provocation, she emailed the parents to say that she was still waiting to find out the details, so I feel like she jumped to the conclusion that boy B must have annoyed boy A and caused himself to be hit.
The children are 10/11 years old. According to DD boy A often does things like this, though its the first time a teacher has ever told us.