[daemonologist]

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.