While a lot of this discussion is 'useful' it is not relevant to this topic and more suited to the 'Safety' forum. Coming back from cloud-cuckoo land, let us remind ourselves of the actual situation. Aircraft on stand, engines shut down, APU power (possibly GPU? as well?) and 230 passengers standing, retrieving overhead items and disembarking via Door 2L onto a jetway. APU then shut down, so possibly a/c semi-dark on emergency lights?
So, all this guff about passengers arriving at 'burning' or 'running' engines, or 'meat grinders' or 'still airborne and opening doors' etc etc is NOT RELEVANT TO G-BYAT. In the circumstances, apart from the risk to pax from slide use and apron hazards (while there was no actual need) there was no hazard in ordering an evacuation and those risks would equally have pertained if the evacuation had been ordered by the flight crew. If we are to discuss this sensibly we need to understand the situation in the cabin properly - and we STILL do not know 'the truth' about what the SCCM did or intended to do (or why, really), nor what actual response she was getting from the Captain other than an apparent lack of two-way communication.
I suspect there were issues on both sides of the flight deck door here. Things could obviously have been done better. Perhaps one day we will find out what really happened? In my opinion there is undoubtedly more to this than meets the eye.
So - lessons learnt? SOPs reviewed and reinforced where necessary? Recurrent training has a new topic which will certainly revitalise what can be dull hours.