That's interesting, I assumed the reaction was rapid but I didn't see it happen. It's not obvious in the pics, but 2 stacked cells in the pack swelled, so I assumed it involved an electrical issue.
Related question - best way to safely dispose of old LiPo batteries? I don't want to just toss it in the regular trash (for one thing, might ignite in there.)
I.r.o. the latter question, ask the local recycling company.
Batteries are a fire hazard and a heavy pollutant if thrown in the regular trash, but most of the raw materials can be recycled if disposed of properly.
Related question - best way to safely dispose of old LiPo batteries? I don't want to just toss it in the regular trash (for one thing, might ignite in there.)