Does Sleep App Communicate with Garmin App (or vice versa?)

Have linked a garmin smartwatch to my sleep app to track my sleep (though not every night - I find it irritates my wrist). Noticed that since I installed the Garmin add on, it “looks” for the watch when launching the sleep tracker even if the watch is not connected to the phone.

My question is: does the app communicate to the watch when sleep ended, even approximately? The sleep times between my garmin app and the sleep app are close (though not exact).

Am just curious. This wouldn’t really affect anything I am presently doing