My car also supports the same functionality for Android, with all the permissiveness that goes with. I can only presume there's isolation between essentially an external display for the phone and the car's core features.
Yes, especially in the case of CarPlay it's just a second display streaming protocol. Additionally, most auto nav systems run on a separate CAN (Controller Area Network) bus although this isolation is usually extremely leaky and not particularly secure (the "gateways" linking the system are often full of memory safety exploits at best or simply pass malicious messages between buses or don't verify anything at worst). But in short, jailbreaking your iPhone is much more dangerous for the security of your personal data on your phone than the integrity of your car.
