Exactly right.
CO2 should be standard fare in automotive shops for precisely the reasons you state (and I stated back in post 32 of this thread). We have two of them in our home, as well as a water hose at the ready. I acquired those CO2 extinguishers because I saw what a dry chemical extinguisher did to a kitchen and adjacent rooms after the homeowner used one on an oven fire. It wasn't pretty and it was expensive to clean up.
One of the main advantages of CO2 in an automotive application is that the expanding CO2 will not only deprive the fire of oxygen and snuff it out instantly, but it will also very rapidly cool the hot metal in the area of the fire, making it very unlikely that whatever it is that's burning will re-ignite when the CO2 stops.
Frostbite injury of the foot from portable fire extinguisher [eScholarship]
If this particular fire started while the vehicle was on a lift and there was a CO2 extinguisher closeby, it is more than possible that the fire could have been extinguished so fast that the damage to the vehicle caused by the fire would have been inconsequential and inexpensive to repair. And with that economically different result, the dealership may very well have promptly proceeded with the repair, swallowed the cost of the parts damaged by fire, and finally charged the owner only for the repair -- which is what the owner fully expected when he brought in the vehicle.
In a legal proceeding I would mention that, even though a CO2 extinguisher may not be required by law or the dealership's insurance company, the dealership was negligent for not having one at the ready for a vehicle that was known to have a flammable-fluid leak that was quite possibly located somewhere in the engine compartment. The fact that, even knowing this, the dealership then allowed the engine and attached parts to heat up
Ignition > Autoigntion > Underhood Surface Temperatures
to a temperature well above the flash point of that liquid
http://www.kmcoinc.com/DOT4%20Brake%...S%20(9-09).pdf
is blatant negligence and even a bone-ignorant adjudicator will almost certainly agree.