Check the Apple Watch Users Guide - Safety, Handling, & Support - Important Handling Information
You're right on the first part. I don't think anyone said Apple improved/invented IPx7. Not sure how you figure the watch is more resistant than Apple led people to believe. Apple described the watches capabilities exactly as they should. Naysayers believed those capabilities to be less than what they are just like supporters are looking at these "tests" as proof of higher capability. They're both wrong.
The more exposed the watch is to water, the less water resistant it becomes. A "test" done out of the box is not indicative of the level of resistance 6 months from now.