I think this was done to get the PWA in the App Store because otherwise it wouldn’t add any value over just using the web version and therefore not be allowed in the store.
The native app has tons of extra functionality than the PWA due to access to native APIs. But yes the watch app was done to get into the App Store because the app “has to sufficiently differ from a web browsing experience.” (Which imo is dumb, tons of apps on the App Store don’t differ from a web browsing experience, they just show pictures in a feed…)
Anyways keyword “sufficiently”… Building the watch app was the only thing I could think of that would meet a conservative definition of “sufficient”.