Every time I connect to a Bluetooth device, be it my headphones or my car, or a Bluetooth speaker, Spotify automatically starts playing on its own. I've contacted Spotify about it and they say that it's a problem with the phones software not Spotify itself. There's got to be an answer somewhere about how to turn this off. Or an option created to disable it as it's very annoying hopping into my car or putting my headphones on and my music blasting all of a sudden. The same thing happens with my phone calls. If I have my headphones connected and then I get into my car I have to tell the person on the phone to hold on so I can switch the audio back to headphones. There should be options in the Bluetooth settings for the device for these types of things.
For music automatically playing in your car check android auto settings. Search settings for android auto or go into Settings>connected devices>android auto>start music automatically, make sure this option is turned off.
