If the perp was sitting under the wrong tent, I would look to any bullying as coming from his own hs. As in someone chased him off, or he just couldn’t be around them. Someone who is bullied may be at the point of carrying a knife to potentially hurt his tormentor.
He finds another tent to sit and collect himself. The story is that the victim asked him to leave. That could range from “hey buddy do you mind not sitting here” to “get the f out of here you piece of shit. No one wants you here.” At that age, if a friend said the former, I would later describe that as asking them to leave. Then the perp snaps at one more person making him feel small.
you can say one thing to someone and all of their pent up anger can go against you. It’s not right but it happens.
edit: also if an athlete is sitting in the wrong tent, something is off. An adult (coach?) should be asking questions. I never was around track but spend more than a few weekends at hs basketball tourneys. Understaffed coaches pretty much allowed us free range in between games. In hindsight it was a recipe for problems.