They're on an proprietary extension of Bluetooth, standard compatible but closed to their devices. They usually don't talk much about it, Phil Schiller was the most explicit I think (it was about the airpod's W1 but it's the same deal)
The short answer is yes, it's proprietary shenanigans. Apple likes security for Apple peripherals connected to Apple iPhones, and they consciously undermine security of anything else.
