Youtube video available of the Firefighters showering the battery with water after the fire: https://www.youtube.com/watch?v=qqRIf4uP1W8
Lithium Ion batteries are dangerous chemistries that are "protected" by electronic computers soldered onto the batteries to keep an eye on voltage/temperature/etc. etc. But in extreme circumstances (such as flooding, or great impacts, etc. etc.), there's nothing that computer can do to prevent an explosive result. Once a Li-ion catches on fire, the electrolyte is itself explosively flammable, and things get out of hand very quickly.
These sorts of events will be common as Teslas (and electric cars) exist within catastrophic zones. This explosive reaction is larger, faster, and more dangerous than even gasoline fires. Doubly so with the "Electric Locks stop working" issue in Teslas (and since manual releases are so difficult for so many people to figure out, many people have already died by getting locked into a Tesla electrical fire).
Fortunately, no one was hurt during this particular incident. But it is a good reminder of the dangers of this particular chemistry.
Solid State Batteries are likely the next advancement that can hamper explosive results like this. So I think EVs have a way to fix this problem in the long term. But today, with today's level of technology, we have to keep this explosion risk in mind.
Remember, if the battery and power module were water proof, this wouldn't be possible. Tesla denies warranty for water ingress in motors and battery packs regularly.