I don't understand how this is possible. Trains are single track in most subways and metros, and definitely do not stop before an already waiting train.
I think the implication is that the time between two trains was little more than the time it took to walk along the whole platform, which the friend still had to do after getting off, plus someone familiar with the stations not needing time to orient themselves and find the intended exit.
i ran down the platform and, without any other waiting, climbed on the first car of the next train
they got off the last car of the first train and started to walk in the same direction as the train. while they were walking, the first car of the next train, me, rolled well past them before stopping.
