Mystifying conundrum about tracking lost airpods case

Hi, I left my airpods case on a London tube carriage about 21 days ago and I can see still them going up and down the tube line. They move every few minutes and remain stationary at the end of the day when the tubes stop running.

Is it possible my airpods case is still on the tube carriage (down a crevice somewhere as they haven't been handed in)? Can the 'Find My' signal be sending to my phone this long after they were last charged? The tube staff think it's some kind of 'ghost' signal but I don't think that's possible.

Please help!