Considering the offending kid could have an allegric reaction to peanut butter which can be very severe. I think the other kids should be punished as well. :~
Otherwise I would say the offending kid did a good job in one uping! :D
He should have resisted the temptation to brag--the victims don't seem to have realized what they ate. He could have avoided the consequences and still have lived with the warm and fuzzy knowlege that his tormentor had received his "just dessert." :)
OTOH, due to media coverage he now has irrefutable documentation of the prank, and has thereby secured perpetual bragging rights if he goes off to college.