The demonstration video makes it appear to be "harmless", but scale it up in capacity and you get thing like
THIS result.. And that ISN'T the "first time" it has happened to a megapack and won't be the last time either.
In 2021 Tesla was reported to have moved over to LFP batteries
HERE So, the one that caught fire might have been older Lithium tech, or it could be the new LFP.. No one outside of Tesla is going to know for sure..
Folks like to think they (new Lithium versions) are 100% "safe" but the reality is they need to be respected due to the very high energy density they can hold onto in a small lightweight size.. The video reported max of 250F, that can ignite a lot of stuff like plastics and cause severe and possibly deadly burns to a human or animal.
Treat em like toys and someone will eventually get hurt.