No idea how Apple works this out.
With Google/Android if I connect my Android phone to an ISP router, with default SSID, and enable all the relevant location permissions, Google will pin that SSID you that location.
If I stood in the street some time later with a different phone, with GPS/3G/4G location off, and only WiFi location on, it directs straight to my house.
I've noticed this over the years and changing SSID used to lose the ability to get location from WiFi only.
However now I have so many unique ISP SSID's around me, any device be it Apple or Android, is pretty accurate at working out the location using WiFi only when in my house.
I used to use an SSID of BASE.
WiFi location wasn't as accurate with that.
I imagine that's a common SSID.
You could try changing SSID to something unique if it isn't already, if you want it to be more accurate.
