At work, whenever we design hardware that uses Li-Ion cells, I always discuss safety before we even have done the design work so that we build something that is safe. Why did these guys not do that? Did they only learn about videos of li-ion explosions/fires after design this?

By the way, they probably should have used a LiFePo4 chemistry instead. It would not have the same runtime, but it would be much safer in worst case scenarios.