These things unfortunately happens rarely but regularly ( wrong bus at outside position , change of aircraft last minute , swapped crew briefing papers, change in planning message stuck somewhere , etc..) but almost all the time it is discovered either at boarding ( F/A checking boarding passes,) or at first PA announcement before of while taxiing ( our flight time to xxx is ..) a very rare couple of times right after departure , again after a Crew PA announcement, therefore it is very rarely ending at the wrong destination.
I would bet, you will find in this case a lot of holes in the cheese , and the fact is as well that today these kind of things end immediately on twitter and are picked up by media...