All these "waterproof" implications are a disservice to the community. All they show is that the watch will tend to be fully functional after a period of time under water. However, even if electronics survive the initial plunge, it doesn't mean the water intrusion won't continue to work against the guts of the watch if any got inside. Apple has stated explicitly that this thing is NOT waterproof and recommended against even some scenarios where water resistance (not proofing) should be avoided or minimized.
Every one of these "it's waterproof"-type suggestions should have an asterisk with the fine print saying "check back in a few days, a week or two and a month because implied results may not be representative of actual results with a little passage of time".
A flooded house can have the internal visible parts cleaned up to look as good as new. But the water intrusion is probably also working behind the walls, growing mold over a period of time.
Irradiated humans can seem fine right after exposure. It's only some time later that their hair starts falling out and the other effects of radiation poisoning show.
Water intrusion in electronics is not always immediately & obviously damaging. But mix that intrusion with a little passage of time and see what you get.
Apple has said "NOT waterproof". 50 posts of "I sent mine down to the Titanic and it's still working" doesn't make it reliably waterproof. All that each of these scenarios implies is short-term luck... like the guy who claims his flooded house is "back to new" after the flood or the radiated people "are fine" immediately after the event. Check back again some time later and see if that luck persists or if the reality of chemistry and physics have set in.