Bullying is systematic and continues over a period of time. If a child makes one bad choice, it's not yet bullying. It's an important distinction.
It is still an extremely bad choice that needs consequences so that it is not repeated.
I while I agree that one incident doesn't make a pattern, bad choices not nipped in the bud can become patterns of behaviour.
Also, I think if you asked the kid that had their hat stolen or forcibly borrowed I bet it felt like bullying to them because it also meant that they couldn't go out and play outside in the sunshine.
