Not sure what the discovery is. Haven't social sites been doing this since the beginning? Reddit was. Not too dissimilar from those IP ads from like two decades ago, "Jane Doe is ready to meet you in Centralville, Wyoming".
I still find it surprising that this is new news as it has been the direction of different industries for a couple decades now.
When I got to NYC on the other hand and attach to public WiFi often those localized ads are spot on to within a block.