ICE cars do catch fire just sitting parked now and then, just like EVs. Electrical defects are a possibility in any car. HEVs may be the worst in that they combine all of the elements of a BEV and an ICE in one package.
Now, think of how complex a typical vehicle is, built up of thousands of bits and pieces which are often supplier assemblies built up out of hundreds of pieces each.
Lots of potential for things to go wrong, since defects in components and assembly will inevitably occur in some proportion of completed vehicles.
Finally, I can tell you from the years I spent as a volunteer that cars burn just great and after a couple of minutes are usually a total loss. It does not surprise me that the shipboard firefighting system could not keep up with the conflagration, and BEVs need not have been involved to bring this outcome.
Also, you can't just witlessly pour water into a hull unless your intent is to sink it through downward flooding, or capsize it.