I think that was the OP’s point. FB woule have geolocation information on you because thanks to someone else’s use of your WiFi network on their cellphone, FB c

I think that was the OP’s point. FB woule have geolocation information on you because thanks to someone else’s use of your WiFi network on their cellphone, FB can now associate your IP address with a geographical location. So even though you’re on desktop and haven’t provided them with location permissions, they can still identify your location based on your IP address.