Perhaps the cars compatible with Android Auto have compartmentalized CAN buses so the audio system is blocked by a gateway from the engine control hardware – although reprogramming controllers on the bus to bypass these defenses is possible.
Are you kidding me? That would require a level of security awareness and defensive programming which you are not likely to find in an embedded software and hardware engineers in consumer (and vehicle) electronics space.
They take pride in how much cr*p one can shovel to run in real time on one measly CPU instead of separating functions onto a couple of units and thus reducing the complexity. The end result is stupidities like a 50K car allowing you to program new keys with a 20£ gadget despite the fact that the alarm is activated and the car is supposedly in lock-out mode (hello BMW) and in more recent days connecting an unprotected fully opened CANbus implementation to the Internet with no security whatsoever (hello Crysler-Fiat).
It is not that difficult to do a CAN to CAN translation and/or forego CAN as presentation on the USB altogether and lock-down the CAN in the USB-to-CAN controller (the car providing to the stereo USB presentation, not CAN as we know it). However, you are more likely to make all 3 faiths coexist peacefully on the Temple mound first before you make an automotive engineer design and implement this correctly as a security measure against an attack coming from the infotainment unit.