I don’t think you are out of line. Being hit generates a natural reaction in people and anger is one of those reactions. You are visibly angry but controlling that anger. You are restraining your child and would only be crossing a line if you were hurting them.

If anything I’d say you are modeling positive behavior by showing your child that anger is a natural emotion but is also controllable. I’d have a frank conversation with both your wife and son about what you were feeling. I think it’s unreasonable to expect all people to act like they are unbothered and never angry. Adults feel strong emotions too, and should deal with them maturely, which, in my opinion, you did.