At first, I was thinking this was the age old feature of "shake to shuffle". I've had that feature off for a long time now, and was just reminded through settings options that that is no longer a thing.
When this is happening, is it only relevant to connecting to your car and does it shuffle your entire music library or just the album/playlist? When my phone connects to my car, it tends to trip over to playing my entire library starting with A Lack of Color...overshare, but I hate hearing that song now because I know it means I will have to tell my Music app to stop it and play something I actually want to hear.
As a counter to this event, you could prompt Siri and say "turn shuffle off" when this happens. That way you wouldn't have to fumble through your phone while driving.