I thought the same thing. I just backpacked with similar foods for days and was fine.
But maybe those were shelf stable to begin with? (Like shelf stable meat sticks).
Do remember those other kids at school are exposed to tons of germs and many put their hands in the mouths constantly. Also I’m sure the hand washing is less than clinical for kids at school too. Plenty of stuff to touch. Could be anything!
I am sorry that’s happened. And I do hope he’s restored now!