This isn't a phone thing, it's a car thing. Google your car model / year and how to turn off auto bluetooth playing. Some cares let you turn this off, some don't.

if you can't configure it to not play, you can get this track https://www.engadget.com/2017-08-10-silent-10-minute-song-itunes-car-stereo-trick.html -- it's a lame solution, but i guess it works.