The smart money around here (one lives near Grand Lake of the Cherokees, an easy day drive from the Tulsa/Owasso area) is saying what the medical examiner isn’t saying but might be implying - “Self-harm”, to put it politely.
Note that one said MIGHT be implying. Nothing has been said officially, and toxicology reports are a couple of weeks out.
OTOH what we do know is that the kid was the victim of some very sick adults.
That would not be unexpected for some poor kid that tormented.