This happens sometimes. It depends on the precise details of the Internet setup. Sometimes your Internet Service Provider re-routes or otherwise "rewrites" your exact location. I see it all the time on my end, where it appears that I'm browsing from a location several hundred miles away.
If you use something like a VPN, or maybe even a feature in your web browser, the same result can occur. A VPN might even be in place without your knowledge!
In short, the data you see in CK is surely a best-effort attempt by the CK folks to guess where your subscribers are when they join your list, but it might be wrong in some cases. And I think that's just the reality of the internet these days; I'm not sure much can be done. I'm actually not even sure if you can manually reset the location of a subscriber. It seems to be data that gets set once and never again.