It would probably be more accurate to say the battery caught fire, which hasn't been uncommon with Li-ion batteries over the years. Laptops have also been known to catch fire, as well as many other items with Li-ion batteries including some electric cars. Tends to be caused by failures in the controller circuitry in the batteries. It really does pay to pay attention to the warnings when using this technology; I know Garmin warns about leaving their units in the sun (which seems a little strange when they have you mount them to the windshield of your car, where of course there would never be any sun and high temps, right?). We definitely remove ours from the dash top mount and disconnect it from power whenever we leave the car, both because of this potential issue as well as the obvious desire to not make the car a target for smash and grab thieves.
I think about this sort of thing every time someone starts a thread asking about the Li-ion batteries being hawked as replacements batteries in motorcycles, especially the ones made with cheap Chinese components.
Jerry