That's why I keep harping on the sound system being the culprit - or at least a contributing factor. Extension cords, power cords and strips and electrical outlets can only carry so much load before they overheat and potentially start burning. It may have been the fridge that went first - a witness said they saw flames behind it - but it also could have been an outlet. Heck, or even a cheap, light guage extension cord.
In the June 4 video you linked to, at 6:24 it appears that the sound dropped out. Many audio devices (but not all) have onboard circuit breakers in case of surge or overload. Given the age of the building and the fact that they also stole power from the store next door it's pretty clear the wiring was probably a mess. Our old house has some funky wiring too and while we were able to upgrade much of it we ended up installing a whole house surge protector just in case. And sprinklers, smoke alarms, a FA system and two extinguishers, lol.
That warehouse had none of those. I took a quick look at the codes and if I understand correctly, if the walls were made of one-hour fire resistant material they could squeeze by w/o sprinklers under certain circumstances. I doubt if that was the case at the GS though. 30 years since any inspections? Oy vey!
Anyway, Foxfire could probably explain it all better.