Google is very hard in alot of ways, let me explain some factors how it might have found your location:
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your device might have been finger printed this can vary from browser to even hardware finger printing.
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once it got a hold it tries to track other devices in your network, and it might be learning about your traffic (search history) with counters very similiar as how AI does it to identify a pattern which is required to identify a device to your location.
Often when one device had used a search, or was logged on google services, and you did replicated atleast a few of these steps on a different device, your region will change in your address if that was set.
So if dnsleaktest shows no leaking of your isp dns, and killswitch works properly they either used a client side request to your browser to get the data to fingerprint you inclusive country and maybe even phone location data, or they use the search history / and or pre existing cookies from webshops with scripts to google to gather a identity they link to.
Note that some devices ignore dns settings especially android devices still want to connect to google dns and ignore manual settings, make sure to override dns in the router ui.
And the only other thing what might ‘work’ though maps is different, there are alot of chrome addons which keeps writing bogus as a bot into the search field, I did had a little success with this a year ago but I’m not sure if it can affect maps.
They use really sophisticated ways to track you😋