She was likely inadvertently non-compliant or holding up the line and the attendant over reacted or actually pushed her.
What you can see on the video is a captain standing there like a bump on a log. That situation could have pretty easily been contained by him taking control of things.
That is, helping the lady to her seat, having attendants get her a coke or bottled water, walking right up to the phones recording and people and saying, “I didn’t see everything, but let’s get everyone settled in and I will get to the bottom of this for everyone at the end of the flight.”
Yeah, the bald attendant seemed like he was the one in charge.