I'm pretty sure it's not the fall they're reacting to, it's likely the sudden ear splitting shriek of the train brakes that the operator was forced to engage to avoid running those two over.
A woman's boyfriend left her for another woman so instead of going after the guy, she met up with the lover, blamed her for ending their relationship (as always logic was not a factor in this). They got into an argument, and then she tried to kill his lover, apparently. I'd assume the bystanders didn't react initially because the two had been squabbling and they likely didn't realize it had escalated into an attempted murder until it was too late
https://youtu.be/PINQHhWkkVk
https://youtu.be/PINQHhWkkVk