Old mushroom lover here too and first off chocolates suck. Almost certainly less than 2g in each. If you ate 2 or 3 however that could produce a level 5 or above trip... but so what?!?!?! Mushrooms aren't that powerful that they can control your mind like that. It's still YOUR mind. Eat enough shroomies and eventually you'll figure out that you don't need to eat shroomies to trip. Whatever happened was NOT the fault of a drug.
Quick example for purposes of comparison: I have a friend who, despite the fact that he is a nice, kind, and gentle person when sober, gets all sorts of belligerent and violent when drinking. It's not the alcohol's fault he gets like this... it HIS fault. It's in him already and alcohol just brings it out. He should get help, and he should know better than to drink given his inner anger issues. This, I believe, is the case with all drugs. We have no proof (yet) that this kid ate shrooms but even if he did that doesn't mean shrooms are to blame... it just means that he had something going on in that head long before the cubes arrived. Just my opinion. But do I blame him entirely? Nope. I blame our incompetence when it comes to preparing our children for what they will inevitably encounter when it comes to mind-altering chemicals.
As a society, we fail our children (and yes I am a parent) by keeping drugs a mystery. If we are truthful with ourselves we have to acknowledge that every single one of our kids will encounter drugs.... every single one. Not all will try them, but many... I believe most... will. But even though we know this we are so scared to talk about drugs with our kids, they are so taboo, that all we can manage is to quote some stupid slogan like "just say no" and then we send them out into the world with next to zero useful knowledge of what chemicals are out there, what they do, what the dangers are, what the benefits are, how they should be done if one chooses to partake, what things not mix, what environment to do them in... you know, all the knowledge that would enable people to make better, more responsible, informed decisions and lead to a safer period of experimentation. We don't do this however, instead we just send our kids off to college or out into the world and effectively say "hey, figure it out through trial and error. Good luck." Then shit like this happens (if indeed drugs were involved which they probably were). Like GI Joe said "knowledge is power" and a little education may have prevented this horrible incident.
Oh. One last thing. There really is no proof that mushrooms have been used for thousands of years other than by the Aztecs who used to ingest a similar, but different species than the ones commonly consumed for recreation today that is actually a lot more potent. And unlike the "flower-power, coming home feeling, merging with the universe, everything is connected" feeling many users describe when eating shrooms, after the Aztecs ate shrooms they proceeded to rip the still-beating hearts out of people they were sacrificing to Gods that don't really exist (and I realize that saying 'gods that don't really exist' is redundant). All those cave drawings of what look like shrooms growing from masked men (mostly found in Europe) could be interpreted in lots of ways... not just mushroom related stuff (ie spears or arrows). It is POSSIBLE that ancient cultures partook in hallucinogenic mushrooms, but any dispassionate scientist would agree that there is not even any good evidence for it (outside or the pre-forementioned bat-shit-crazy Aztecs). Recreational use of hallucinogenic mushrooms is a phenomena that most likely emerged in the past 50 years.
Phew. Sorry for the rant. Gonna make a cup of tea now (the normal kind!)
Oh and while we're at it, while we know for a fact that the Aztecs used shrooms, we don;t blame the mushrooms for their violent, bloody sacrificial ceremonies... we blame them! As we should.... the mushrooms didn't make them do it. Their own minds which had been warped by their fucked up religion and society did.