This may be one of the few occasions on this forum where a non professional's view might help
As an 'interested' passenger and private pilot who has followed airplane and airline progress for over fifty years I can tell you that the functional difference between 'Disembark' and 'Evacuate' had not really occurred to me until reading about this incident. (Of course I know the 'literal' difference.) Younger people who have no interest in airplanes other than how much it cost to 'get there' wouldn't have a clue, and certainly not in the heat of the moment of an apparent emergency.
As three of my kids went through armed forces officer training a few years ago I was struck by how much of that training was about communicating precise instructions. Basically if you have not told someone exactly how not to screw up they will inevitably make the screw up choices.
The question will be how to tell passengers that you want them to disembark quickly and without their possessions without them jumping to the conclusion that it is some kind of emergency.