Stop, They [Over]shootin'
We could overhear parts of the conversation between MTA employees through speakers in the train cars:
Partner, we a Z.
Partner, did you pull the cord?
This train is being discharged.
I am assuming this was a two-way conversation. It's possible the person being referred to as "partner" wasn't saying anything. Maybe they had totally dozed off, which would explain the situation.
J or Z, it didn't matter. This train overshot the station.
On an elevated track, if the doors had been opened, people in their programmed rush to exit would have tumbled to the street.
MTA employees came through the cars one by one to manually open a single door in each, through which every passenger grumbled and exited.