^^^ that should work. I just checked and I have those settings, too (Android 8.0 on an LG G6). My wife has an S7 Edge, so I can check for you when she gets home from work if you'd like. The only problem here is that if you ever want to play music in your car, you have to go back and manually turn it on and then remember to turn it off again.
Another thing to try would be to use your car's hands-free settings to select the music player, if that's an option. In my car I have my phone and an iPod nano paired. If for any reason I was using the phone as the audio source and forget to switch it back to the nano, it will behave exactly as you describe. Once it pairs, it launches the music player, even if i have the head unit set to the radio.