The difference is you can extinguish a fuel fire by smothering it. Deny it oxygen and it can't combust. When you do that with a battery fire, it just flares back up as soon you stop smothering it
In theory you're right. On practice - until you're an equipped firefighter, you wouldn't be able to do anything once a regular car develops significant fire.
You can absolutely extinguish a fuel fire early on if the tank has not ruptured. Sand, baking soda, water, dirt, blankets, all work. If the battery on an EV develops an entire short you are not extinguishing it. If it were available, the safest mechanism would be to push it into a hole and bury it
Eh, a 5lb extinguisher in good hands has enough punch to extinguish a flaming stock tank of diesel twice so it should put out a car that isn't totally engulfed.
Source: Got to watch a demonstration put on by the local firefighter training center.
Source 2: Anecdotal experience buying burnt out vehicles at auction, the state trucks with extinguishers are typically only a little burnt.
