On Android (ie meaning the OS, not the android version of the FB app), the wifi and bluetooth perform periodic scanning in order to provide better location services, it's said.

I think this is helpful especially in urban environments where the raw GNSS position is very rough, but typically several wifi APs are broadcasting, so the RSSI of those APs beacons helps to reduce positional uncertainty.

Th scanning is performed even with BT/wifi turned off. You can explicitly turn the scanning off in some settings submenu.