The assertion is that EV fires are not particularly more difficult than ICE vehicle fires if the battery has not entered thermal runaway.
Most EV fires do not start in the battery (at least for EVs that are not involved in a collision).
And while the battery certainly can enter thermal runaway by an external fire heating it up sufficiently, it's not a given as real-world examples like the Sola fire shows as well as various research. Here are some quotes from a paper about full-scale EV fire tests[1]:
In both cases the fire ignition took place in the rear seats. However, it has to be mentioned that in the case of the BEV, the battery was not involved in the fire for the first 800 s (full voltage in all cells of the battery).
However, the test also showed that although the vehicle had already burned for more than 10 min, the battery was still not involved in the fire and the temperature inside the battery was well below 50 °C
In the tests they forced thermal runaway after a while, by shorting the batteries.
Here's[2] another, smaller study where they tried to initiate a thermal runaway by placing a propane burner under the battery, but failed as they removed it too soon.
The burner was in place for 12 minutes, at which point the rest of the car had caught fire which also contributed to heating the battery. Yet no thermal runaway occurred.
Modern cars, EVs and ICEs alike, have more flammable material in the form of plastics than in their batteries or gas tanks[3]. And those plastics also release a lot of toxic smoke when burning. Sure, if the battery catches fire it will release nasty HF gas, but it's not like fumes from an ICE fire is healthy stuff.
[1]: https://www.sciencedirect.com/science/article/pii/S037971122...
[2]: https://www.fireproductsearch.com/full-scale-electric-vehicl...
[3]: https://www.europeanfiresafetyalliance.org/wp-content/upload...