Capsaicin is a very selective neuro simulant which kills insects by locking up their nerve systems. Sort of like strychnine for bugs.
It may be quite possible for some individuals to be unusually sensitive to capsaicin, to where they could ingest a lethal dose that would leave other people unaffected.
Think of peanut allergies as an analogy.
I would not be surprised at all to find that this kid died from the overdose of ghost peppers, probably from a lockup of his intestines followed by a cascade of circulatory blockages.
How many chips did he eat?