What is the suspected method of Bluetooth communication?
Afaik phones do not share their internet blindly to Bluetooth devices.
Bluetooth PAN seems to work pretty seamlessly once you've paired your phone and set it up. It's possible some kind of "seamless hotspot" functionality is remotely activating PAN on a paired device.
Also thought about it. It’s possible, but requires enabling hotspot on the phone. Without it, it will not share internet via BT.