Are you sure about this? I seem to remember connecting my iPhone to a rental car and realizing that it had transferred my contact list into the car somehow.
My iPhone has asked me before if I want to give my contacts to a car, it’s never done it unless I said yes.
That is a Bluetooth feature.
That's if you connect it over old-school Bluetooth, and it shows a permission prompt asking you if you want to do it or not.