Nope. You an put a lead-acid battery underwater and it won't catch fire. It won't work anymore, but it won't catch fire.
Gasoline does not explode if contaminated with water.
You put a lead-acid battery in water, and it will spark, and catch fire. That fire will spread in time to the gas tank. The explosion from that will be far greater than anything that can come from most EV's.
Gasoline does not get "contaminated with water". It does not mix with water, but instead floats on top of water. That creates a very dangerous fire/explosion that spreads quickly. It is basically impossible to put out with water, and will spread quicker with water. A car in a flood can easily destroy a very small town, and a gas station in a flood can easily destroy a bigger town.



