Why was the kid in the other team's tent in the first place?
Credible suppositions from the various quotes available - and NONE of them may turn out to be correct! - are that the assailant had left school to go back to the track meet earlier in the morning, and was found inside several teams’ tents. Rifling bags and going through the other track meet teams’ stuff. Stealing phones, wallets, cards? Likely.
Anyway, he was discovered, and was thrown out of the cover.
Left, went home and got the knife, returned to the track meet - still not in school. Was discovered again going through more bags, was thrown out (again.) Then drew the knife and killed the victim.
Would be premeditated, planning on violence after he went into the tent a second time. Could NOT be an accident. Nor a “misunderstanding” or “lost and hungry” innocent boy.
I will maintain that if a person wants to protect himself, just brandishing a knife might’ve been enough. If it didn’t stop, he could have slashed an arm or leg. This kid went for the heart. That to me means he intended to kill the other teen, not just defend himself.
More like premeditated because he went back home and got the knife as you claimed, then went back.