& the firies couldn't put it out?
Vehicle fires take a surprisingly long time to extinguish for the lay person standing on the side of the road watching their car burn.
By the time we arrive at them usually 5 minutes + after the call most cars will be well engulfed in fire (which is why I always carry extinguishers in my 4x4 - as this allows the possibility of action before it is too late). Almost everything in a car will burn from the seats to the tyres and produces acrid choking smoke (hence why our standard operating procedures call for the use of breathing apparatus).
The majority of fires start in the engine bay which has numerous nooks and crannies and is often liberally coated in grease, oils and other flammable liquids.
Assuming the engine bay is on fire the first task is getting into the engine bay, which isn't as easy as it sounds especially on modern vehicles especially after a front on collision when the area is engulfed in flames and the release mechanism is jammed.
Once the bonnet is open we have far easier access to the seat of the fire and can liberally douse the flames, usually with water alone. On some of the larger fires or those on trucks with hazardous loads with a foam solution until such time as we have cooled the vehicle enough for it not to be a risk of reigniting and allow the towies to remove it safely.
I have attended single vehicle fires before where this has required 3,000litres + of water to achieve due to the fact it was fully engulfed from the tyres through the interior to the engine bay. Obviously by this time your little in cabin extinguisher is going to be of no use, but it can certainly help if you can get to the fire quick enough.
(Edited to make sense after my 2nd coffee had cut in)