My first thought was that the driver of the silver car had a medical issue and had their foot down on the gas.....but then we see someone get out of that car later, no minor miracle there, IMO.
I think the fire, initiated by the metal-on-metal impact, was fueled by a ruptured gas tank of the of the red SUV that got rear-ended, it's gas covering the outside of the silver car, so it burned off quickly on the exterior.