On Android, there's a prompt when a paired device requests access to your contacts/call history/messages, and you can deny the request. It's irrelevant to play audio but it allows the car to give you a built-in interface to use your phone for calling and such.

I didn't know that iOS didn't prompt you for that.

You didn't have to do that, though. You can connect Bluetooth audio without syncing your contact list. Additionally, just because your phone is showing your contacts in the car's interface, that doesn't mean anything was synced to the car. It may have just been reading your contacts from the phone via Bluetooth. As soon you as unpair the device, those contacts would be gone, if that's the case...

Thanks for pointing that out possibility because I couldn't find it. I wonder if it's an option for Hyundais because it's not included in their quick start guide either:

http://www.hyundaibluetooth.com/content/dam/Bluetooth/Hyunda...

My Ford does this (sync contacts) by default too. Yes it's an inexpensive car but you have explicitly turn this off and it's not intuitive. Not quite a dark pattern per se but I prefer to not connect BT to rentals for that reason alone.