There is more than one kind of Lithium battery. The kind Tesla in cars use can catch fire if they get too hot.
The car has multiple safety systems to stop this from happening. The raw cells have far less, if anything. There could be a thermal fuse but who knows if the older cells have that.
A single cell isn’t going to cause too much trouble, but I worry about home made PowerWalls and home built EVs using Tesla / Panasonic NCA cells. I’ve seen some DIY projects that appear to have no thermal management.
Even in the car, the batteries do occasionally (well very rarely) catch on fire. To be fair, fires in combustion engine cars are far more common but they don’t get press attention.
Tesla’s Powerwall use NMC cells,. Tesla say this is for improved cycle life but I wonder if it also because they want to reduce the risk of thermal runaway.