Lithium Battery manufacturing is still relatively new. A small mistake either in the design, the manufacturing process, or quality control is a problem waiting to happen.
I can think of several instances where poor design become a problem for ICE vehicles. Corvairs, Vegas, Pintos, some Ford Explorers with Firestone tires.
People died as a result in these vehicles.
Battery tech will get better.
The biggest problem is still lack of Lithium and the run up in prices for Lithium
If there had been people on that bus, would they have had time to get off? I don't think so.
It is not just lithium batteries in buses. GM recalled every Chevy Bolt it ever made because the lithium batteries were prone to spontaneous combustion, and advised anyone keeping the cars not to park them within 50 feet of a building or another car. When one checks in for a flight, they are asked if they have any lithium batteries, and that is because a jetliner went down some years ago in Florida killing all aboard when smaller lithium batteries being carried as cargo spontaneously combusted in flight. There have also been major fires in the giant lithium batteries used for wind / solar storage in Belgium, Australia, and South Korea when the huge batteries spontaneously combusted.
Most buses run on diesel fuel, which does not catch fire very readily and when it does, it does not burn so rapidly. There are much safer electric buses, namely the trolleybuses of eastern Europe, which have a mast that contacts an overhead power line for electricity, much like a streetcar does. I have rode trolleybuses many times and would again, but NOT one of the lithium battery buses.
It is probably wise that Paris has removed all of those lithium battery buses from service, but one wonders what other cities may be using the same bus. Lithium burns very hot and its fumes are toxic. That combined with the speed that the fire took over the bus could easily make it a death trap if people were aboard. A car is not as bad. Some months ago, a guy was driving a Tesla down the street in Pennsylvania and its battery spontaneously combusted, but he was able to jump out and get away before it was consumed in flames. A bus full of people would not be so lucky.