I think it's less likely to be technical chicanery (special bluetooth beacons, wifi SSID scanning, etc) and more likely that your airline just partners with Lyft and directly hands them passenger information.
Change in IP location? If you suddenly jump across the country but your traffic is still coming from a cell provider (so unlikely to be a VPN) Lyft could infer that you've flown, and to which airport.
Alternatively maybe barometer? All modern iPhones have one, but I don't know if apps are allowed to access it in the background (or without location services), and it wouldn't let Lyft tell which airport you were at.
People have asked this question before and there are a multitude of different potential ways. Supposedly Lyft can sync or calendar and in some cases was being sync'd automatically, perhaps it knew from that?
The app might pull accelerometer data in a way that suggests you just landed or were on a plane? Could it be that the cell towers in that area are known to be based at the airport?
Your calendar can get automatically updated from your emails; I imagine Lyft can likely access your calendar.
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Can register geofenced notifications via https://developer.apple.com/documentation/usernotifications/... in advance , The app is not informed (if don't tapping it) and it is triggered by the OS.