would browsing in private mode skew location services data?
The Wifi location database is created by driving round, street to street, city to city, country to country, testing what WiFi can be 'seen' &amp; mapping it to GPS locations.
None of this requires any login to the WiFi, merely noting where it is located.

This can take a while ;) 

In the meantime, someone might move house, from one district to another, &amp; take their WiFi with them. This will confuse the geo-locators until the next time the Wifi guy drives past again.

Alternatively, an ISP may assign a new IP address to a residence's connection - one outside their usual numeric range. This will produce the same effect.
My ISP recently did this here &amp; I "moved" from London to Bristol for 2 weeks, whenever I was in the house, picking up my own home WiFi.