I was sure you would have had an "expert" answer by now. Was teh countdown recorded or did it come from the driver/guard?
I think she's already had one from the
TM‡ on her train the other night. The
PA▸ 's recent update with very limited automatic announcements must have some kind of test or boot-up automatic count, similar to the 'testing, testing, 12345' you used to hear when Tannoy's on stations were playing up. Perhaps that was triggered if the train stopped sharply? I must admit though, I haven't heard it yet!