I've been tracking this off a Telegram group... and there's one thing that sticks out in my mind:
What was the operator of the subway train doing?
Mind me, I'm not from Boston and even after chatting with Bostonian friends, I still have questions. I do know a bit of WMATA's subway operations, though, from observation: The operator opens and closes the doors and is required to lean out and watch the doors open/close. This is so the operator can catch someone slipping in at the last minute and not get caught. If an operator doesn't do this, in this situation, they get fired.
I also know a lot about MTA Maryland's safety policies, including what happens when a death occurs in an accident and it was preventable: the operator involved is fired.
Thus the question. Are MBTA operators supposed to lean out of the subway cars and look down to see if folks are boarding still, of if someone's caught, as they close the doors? If this is policy, what was this operator doing?