When you play audio on your iPhone, the Apple Watch will automatically display the "Now Playing" screen when you use it. If you find this feature annoying, you can turn it off - and very easily. See below what exactly you need to do.
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In Settings, press "General" and then select "Wake Screen".
In the “Wake Screen” settings, tap the settings next to “Auto-Launch Audio Apps” to turn it off.
The next time you lift your wrist while playing any media, the watch face will open instead of the audio app.
If you want to see or control what you hear, you can always press the small Now Playing button at the top of the clock. The appropriate audio application will open automatically.
And if you change your mind and want to see the "Now Playing" screen again, just go to Settings> General> Wake Screen and turn on "Auto-Launch Audio Apps" again. Nice and easy.
Source of information: howtogeek.com