The article says they just use wheel sensors. Most of them time they don't need to be very accurate so that is more than good enough, but in stations much higher accuracy should be needed and so they need an additional correction there. (note that I said should: I'm a strong believer in automated edge of platform doors which require stopping so the train doors align. Few systems in the world have this though)
A number of parts of the underground already have platform edge doors, and train stopping locations are tightly controlled regardless of the presence of platform edge doors.
