In the presentation they mention they are using GPS, and also an accelerometer.
In a Faraday cage?
with any view of the sky multi-band gps is damn good these days, my watch gets good locks through airplane windows even in the middle seat. In aluminum 737s, not compostite frames.
Train carriages, especially older ones, often have metallic windows so they are even worse than a typical plane. Even right up against the window, with the phone directly against it I have failed to get any lock on some trains.