I was with you until "Likely submerged it in water and it was all over". Flagship phones and watches have been waterproof for many years now. I use my iphone and my apple watch in both the pool and the shower regularly with no issues
Ah, but what you're failing to take into account is that there are magnets in the Apple Watch. And as we all know, you drop some water on the magnets, that's the end of the magnets.
I was swimming with my Apple watch in Hawaii, after a couple of days of swimming the side button sank into the case and got stuck. Now the fun began, long press on that button is an automatic call to 911. I had several calls happened and had to explain to a 911 operator why I'm calling but eventually I was able to turn off (shut down) the watch completely.
I think you just got unlucky. It's a mixed bag with "waterproof" phones, but [flagship] smartwatches should be pretty solid. My GF and I both had Galaxy Active watches, now we have Apple watches, we go swimming and kayaking with them, zero issues.
Not as unlikely as one might think. The random inputs, after unlocking the watch with a passcode, might hit the messages app if that is set up as a complication. Then something similar to we are in control is written (drawn letter by letter), which might autocorrect to what OP in TFA saw. Apple autocorrect can come up with some wild sentence constructions.