Parents (with their experience of abut 2.4 kids) and teachers, get incredibly opinionated and tend to vary a lot in their views.
If you're interested in finding out if there might be a reason beyond normal naughtiness, why not ask someone whose job it is to advise on the subject?
10 minute phone appointment? They'll probably say you're doing OK, give a word of advice and say call back in X weeks. Maybe not. Are you afraid of what they'll say? No reason to, you don't have to take notice if you don't want to.
If your mainframe or your car or your heating were misbehaving, would you ask random electricians, nurses and database programmers?
That isn't competent advice.
How are you going to feel if he blinds someone with a sharp pencil, or the second tot knocked off their bike cracks their head open and gets brain damage - and the teacher says she told you so and why didn't you do anything?
There's a bit of CYA to it because she raised the stakes, plus you'd know you'd gone a bit further than you thought necessary to do the best by your son..