eh, I don't buy that at all.... it's mostly steel.. I've seen vehicle fires before.. it's not like a house... seen plenty of small containable ones that never get beyond the engine compartment... but yeah, once the interior goes, it's over... I once saw a 70's Caddy with the engine compartment FULLY engulfed, hoses, belts, plastic all dripping out the bottom, and it never got to the interior..
and the electrical ones tend to smolder/smoke first.. but when you get a fuel leak and the exhaust lights it off, it's usually an engulfed fireball in a hurry..... by the time the fire department gets there, an untouched one is of course a big fireball... not trying to diss a fireman, which I'm guessing you are, but I would assume by the time you guys roll up on a car fire, it's toast the majority of the time...