Turbo, usually the crew would know what the problem was via a NITS or similar tool. If the pilots are giving other info with evacuation command then you are going to have trouble. When the doors are open the cc will have a much clearer idea of hazards than the flight deck.
In terms of the cc situation, as soon as you are on the aircraft or in the area of the aircraft then you are in a work environment. There are a few instances in our jobs that require no questioning. These situations are practiced outside of the aircraft time and time again so when they actually happen they should be second nature. For pilots it includes aborting the take off, going around etc. You hear those words and react immediately, ask questions later when you are sat in the crew room. To hear the flight deck issue an evacuate and not react immediately is very poor. To go back onto the aircraft afterwords is poor. I'm flight deck, in my view if I say evacuate thats all I haveto say. If there's one person or more in the back I do this so I can carry on with correcting the problem in the knowledge that the back is being cleared. If I go incap then its for my co pilot, fire brigade etc to find me.
To issue an evac with a cargo smoke indication is the FD's decision but if the CPT beleived there to be a fire I'm not surprised he shouted when interupted trying to save his life by someone incorrectly following SOP's that should be burnt into their memories.
I would rather someone shouted 'dont open that' when I was about to open an armed door and blow a slide against my SOPs' and saved my job than let me get on with it.
Just to finish, we had a situation in the cruise on a positioner with cc in the rear. The masks dropped as they were enjoying the film, No.1 walks forward to inform the flight deck, opens the door to find both FD with their O2 masks on. They turned around with looks of complete shock on their faces, the aircraft was depresurising, they were trying to get their O2 on and deal with the problem and then they have the incredible extra pressure of worrying that 20 cc in the back are starting to go into Hypoxia.
We practice these drills for a reason, they save our lifes.