I think this is another manifestation of my car being able to detect my key at longer than normal distances. I posted once how my car keeps waking up as I walk around the inside of my house. Somehow the car can detect the key 30-40 feet away. So that's why the music keeps playing after I walk away - I need to walk a long way away to get it to sleep.
It just seems like a dumb "feature" to me. Once I put the car in park, open the door, get out, then close the door - it should just stop playing. Why play the music with the door shut and no one in the car?
So yes, I suppose walking 40 feet away will "work". I just wanted something clever, like pausing music once I am in park and open the door.