Passengers will be contacted and interviewed, I'm sure.
Yes, passengers are as good at thinking as anyone else, but that isn't the point.
Many passengers see things and do not understand their meaning, equally, there are some who are trained.
I am a 747 pilot, if I had been in that cabin I wouldn't have known much either, and I may not have heard the evac alarm if it was cancelled quickly.
It's a long way from the flight deck to the alleges smoke source, it takes a while to assimilate the info being passed by interphone and come to a sensible decision.
BA's current safety training is concentrating on evacuation drills, I have just done it, a full exercise in the cabin mockup is undertaken with debrief afterwards.