But you’d think that in a company that deals in lithium batteries, they’d have established procedures which they’d train employees in.
You could think so! When I was dealing with building li-ion battery packs - and I had, at most, only some 5000 18650 cells at my site, I, just for my own mental health, already come up with some procedures which were more effective than what these guys had. It was as simple as having a large container of water next to the welding robot station, designed as such that the pack being welded will physically fit in said water container, so that I can just push the whole pack into the water within seconds. And coming up with such process cost me just
a few minutes of my time.
It is well known how ineffective regular fire extinguishers (foam, powder or CO2) are against li-ion (or primary lithium, too) battery fires since the cells have internal oxidizers, but on the other hand it's also well known how effective using large amounts of water is, because thermal runaway stops by effective cooling.
Heck, even some fairly small fire brigades have been coming up with ways to submerge whole vehicles in a massive container. Submerging just packaged cells at a factory is
orders of magnitude easier.
Just basic separation of areas stuff; not too many cells in one spot. Companies can successfully manufacture ammunition, explosives, explosive reagents and whatever without these factories blowing up right and left. Just borrow some of the same strategies.
EDIT: Note the above comments of water were assuming li-ion, which in this case seems incorrect speculation. As they were dealing with primary (non-rechargeable) lithium batteries, which contain lithium metal, which reacts with water, using water might be problematic.