It's true that diesel is harder to ignite than gasoline, but statistically they're not much safer than gasoline, and EVs have a lower fire risk than both. Last year, diesel vehicles accounted for 11% of vehicle miles traveled in the US and were responsible for around 12% of vehicle fire deaths. EVs were 3% of vehicle miles traveled and less than 1% of vehicle fire deaths.

Diesel vehicles usually have much larger fuel tanks than gasoline vehicles, so while the chances of a crash causing a diesel fire are lower, the consequences tend to be worse. If the stats are to be believed, the two factors balance each other out.