That story was part of my Crew Resource Management class.
The FA who was (as she called it) “waving like a flag” while hanging onto the staircase bannister came to speak to my inflight training class. And I flew with another guy who had been in the downstairs galley when it happened and a 250 pound beverage cart flew across and smashed into him, crushing his forearm. He had a steel bar in his arm where the bone used to be.