Nobody knows how competent the guy was or what really happened, but from the scant bits we do have, namely the injuries along with the missing switch and battery its obvious something went wrong, likely that the gasses had nowhere to vent, once the pressure was high enough it blew the battery and switch one way and Newtons third law turned the body and topper into an RPG straight into the guy's head. Basically he was holding a device designed to maim or kill on failure.
As vaping continues to grow, as more guys are sold these things without any warning, no documentation, more will get hurt. Its just inevitable. Particularly when new mechs being made every day do nothing to ensure they can vent gasses and don't turn into pipe bombs or (like in this case) RPGs. Placebo holes are easier and give false comfort. Not one mech manufacture in existence has a manual, not even a decent FAQ, how to section or anything to that effect on their websites either, so new vapers being sold these things largely with no warning whatsoever and left to figure them out through trial and error. With the growing user base the probabilities of someone's error getting them killed will keep rising until it inevitably happens.
Demanding manuals, FAQs and proper venting from a mech is a ridiculously low bar to set....
...what's pathetic is that no one is asking.
