We don't use that capability, but the Google Nest Help page below says this:
"Once you’ve set up Home/Away Assist to use your phone’s location, it uses a combination of cellular and Wi-Fi data, and GPS from your phone to help tell when you leave or come back home.
Because Nest only needs to know whether you’ve left or come back, it won’t continually record your phone’s exact location like a GPS navigation app. Your phone’s location also isn’t used to determine when exactly you walk in the door or when you drive out of the garage.
Instead, the app defines a large area around your home called a geofence that acts like a home zone.The Nest app only gets a notification from the location services of your phone’s OS to determine when you enter or leave your home zone.
For example, if you walk over to your next door neighbor’s house, your home may not switch to away because you still may be within your home’s geofence."