After a little more reading, I've learned that many budget Li-Ion chargers (including apparently the TR001) actually go into a trickle-charging mode after the battery is charged and the green light comes on. This is unfortunate, as trickle-charging Li-Ions is not exactly safe. They will continue to accept charge as long as current is applied, and this can lead to overcharging. Overcharging Li-Ion batts is quite likely to eventually cause them to explode. Thus, it is extremely important that batteries themselves include overcharge protection. Problem is, even if they do have such protection, the circuit can fail. With a better-quality charger (charging overcharge-protected batts) that switches itself off after the batt is finished charging, the benefits are obvious...there is double protection...one picks up the slack if the other fails. The question does arise: why do cheap Li-Ion chargers trickle charge, then? I don't have an answer, but wouldn't rule out the possibility that it's just a crappy or flat-out faulty design which continues to be produced simply because it's cheap to do so. In any case, before I buy any other vaping gear I'll be snagging a better charger. In the meantime, will definitely watching for the TR001 green light like a hawk.
I'm not suggesting that this is what caused the OP's boss' incident, though of course it could be...just passing along what I've learned in the course of trying to find out what might have happened.