a building that large would be required to have a fire suppression system in it by any code book in the US. I forget the exact number but something like 95% of fires in a sprinkled building are extinguished with 1 or 2 heads. All that to say they had to have something in there to get real big real fast. I’m going with a bunch of EV batteries cooking off.
If you have several vehicles (EVs) parked near each other and one cooks off, I can see how it would spread from one to the next fairly quickly. A typical sprinkler system would be useless.