You're absolutely right; I've operated a site-to-site VPN tunnel between two locations (tunnel endpoints were on the routers, and both peers were sharing an pub

You're absolutely right; I've operated a site-to-site VPN tunnel between two locations (tunnel endpoints were on the routers, and both peers were sharing an public IP address). After a while, Google would associate the IP address of the local side of the tunnel with the location of the remote side of the tunnel. I assume this is from Android devices connecting to the network on the remote side, being geolocated by Google Play Services, and Google tying this location with the IP address.