EV battery fires are currently significantly harder to deal with than ICE. The concerns are warranted and require fire departments to develop new tactics to deal with them.

Effectively, the batteries hit a point where they thermally runaway, catch fire, and won't go out until their temperature is reduced to below the thermal runaway threshold.

This currently requires a massive amount of water, like on the scale of dumping the burning vehicle into a lake or pool.

However, solid-state batteries ought to eliminate a lot of this concern.