Absolutely, it would irk me. A scuffle, physical contact, etc. is different than an actual all out fight. Especially
since the school thought that this student's behavior and/or history of behaving this way, merited suspension. Suspending a student - especially at that age - is quite serious.
I understand that you can't be informed of every event or every conflict your child experiences. But physical violence is not just "any conflict". As a parent it is your job to address your son's life experiences and use them as a teaching tool. What happened here is one way to turn a negative into a positive. Instead of just this being a "bad" thing it can be a way to educate your son on how to be a successful citizen of the world. There are so many lessons here: how to handle conflict, a bully and even handle retaliation. In my view the school didn't work with you on educating your son.
Think of it in this way: Directly addressing the actions of the other boy (by suspension) and notifying his parents and dismissing your son's role in all of this is faulty logic. If this fight called for the involvement of one set of parents then why don't you rate high enough to be merely notified? Does your son's involvement not merit being addressed? I'm not saying anything more than a "Hey mom, your son was involved in an small altercation with another student. He's completley fine, no one was hurt and although we're not at liberty to discuss another student with you, please know we are addressing the situation. We just thought you should know.". I understand some parents would storm down to the school and rant and rave. But they're going to do that no matter who tells them. That doesn't make it ok to not tell you.
Lastly, what if your son was the type of child to internalize feelings and didn't tell you that he was in a fight and someone physically hurt him? What if this other boy (with a history of aggression) continued to harass your son? When should you be notified? Where is the line drawn. When he bleeds? When your son cries? I don't mean to be dramatic, but really what constitutes "important" to the school?
Sorry for the long rant.
But if this was my son I would be mighty unhappy. And it would NOT be because another boy hit him or even if he got a bloody nose, etc. Things happen, kids fight sometimes, kids get hurt. But I think you not being gently informed is nonsense.