It sounds like he ran the computer without a cover habitually, in order to prevent overheating of the chip. In a modern ducted cooling machine, of course, heat control is better with the cover on than with the cover off. But I have no idea what this guy was running.
There are bits in there that can hurt you, presumably. I am looking at the guts of my computer right now, and am seriously considering replacing the cover. First I will have to find it, since it has not been on in a couple of years.
But I don’t go sticking my sweaty leg in there, or anything...
Computer power supplies generally have their own enclosures within the overall computer case. They have their own fans and the connectors to PCBs and drives have safe voltage levels. They are also usually fused. Processor chips are not inside the power supplies. I don’t know why any dangerous voltages would be exposed if he had the cover off. UL TUV CE would all be exposed to big lawsuits if they let something like this through.
I’m assuming it was a cheap Chinese version of a computer that didn’t bother with a separate enclosure for the power supply. I would say the elegibility for the Darwin may be debatable.