My first thought was it could scan the WiFi names. I think there's many ways to determine location without GPS.
After thinking about it more, I think they somehow know what flight I’m on and are using flightaware or a similar service to know when the plane touches down.
The question then is how they know I’m on the flight. They can do this if you share your calendar with them, but I don’t. The only thing I can think of is either the airline is selling them the data or they’re getting it from my credit card company. Airline flights are unusual on credit cards in that the entire itinerary is on your credit card statement, not just “American Airlines” or whatever.
But I suspect the false positives on this would be huge and if you felt so compelled could easily test while at your desk.
https://developer.apple.com/documentation/corelocation/clloc...
(Edit: annoyingly, the parentheses are part of the URL. I don’t know how to encode them to make HN’s link parser happy, so you may have to add them by hand if you follow the link.)
(Edit 2: fixed, duh--thanks @akovaski!)