like others in this thread have mentioned, trauma is a hell of a beast- but that kind of response seems unusual for a 16 year old, a “fantastical” delusion to cope with the trauma would usually appear in a younger child. if he was autistic or developmentally disabled, had another mental illness, or was mentally stunted by previous trauma etc, however, it could definitely be possible.

someone mentioned hallucinogenic toxins in marine animals- some species of fish can be hallucinogenic only when ingested but AFAIK there is no strong sting that can produce hallucinations. and it just wouldn’t make sense for a marine animal to possess such a toxin. i’m sure you could do something by extracting certain toxins, the “dream fish” when eaten can cause strong hallucinations, and apparently a certain type of sponge can be smoked for a hallucinatory effect... i don’t believe for a second that a toxin was involved in this particular case

i have no idea what type of diving he was doing, and again the circumstances just don’t seem to line up, but nitrogen narcosis can cause delusions, paranoia, and hallucinations depending on how the diver reacts, length of the exposure, depth etc. i don’t assume he would’ve been diving very deep (if he was scuba diving at all) but a 16 year old would likely be unable to respond correctly to the warning signs- even experienced divers can succumb to it. the case lacks a lot of details so i can basically just bring up the idea, this delusion could probably be caused by it? but i’m just a diver who’s never experienced it. additionally i have no idea how he would’ve survived if he’d become unconscious due to NN

since it’s such an old case i wouldn’t be surprised if it was sensationalised, or if the kid somehow just killed the others and made it up for attention. if not, it could be NN or a delusion brought on by trauma especially if he has a history of mental illness. sorry for the long post but i do find this case super interesting and maybe i can provide a little insight. (scuba diver, strong interest in marine biology, and personal experience of mental illness)