I've been thinking about this too, and I think I'm wrong about the Android app. Our cars talk to our phones whether smart or not. The car blueteeth sniff for the phones on power up and both must be pre-programmed with the ID in order to connect. The only difference is that the Hyundai has its own screen and the Ford uses the phone screen for setting up, and any ability of the phones to switch from master to slave is immaterial.
I suspect the main problem is understanding the convoluted command set. I thought one problem is that the HC-05 suffers from a limited set of commands in master mode but, in the matter of Arduino<>Arduino connection, I have been wrong about that too.