The pairing request pop-up is built into every Apple device and is specific to how they handle Bluetooth. Apple forces this to make their products more secure. This pairing request pop-up does not occur on Android devices.
Just works: As the name implies, this method just works, with no user interaction. However, a device may prompt the user to confirm the pairing process. This method is typically used by headsets with very limited IO capabilities, and is more secure than the fixed PIN mechanism this limited set of devices uses for legacy pairing. (source: https://en.wikipedia.org/wiki/Bluetooth)