BTB, the trouble with asking the ground crew if an evacuation is required is that the particular ground crew may have no knowledge of the different ways an aircraft may be emptied and hence may give the crew misleading information. it is not the groundcrew's job to decide that, just give timely and accurate advice.
Dutchroll, hit it on the head... the Captain in this particular situation is damned both ways.
After QF 1, Qantas pilots were told to err on the side of caution where smoke was concerned.
If indeed what BTB relates is the actual chain of events, i.e. a fire is reported with little clarification, the captain is in a invidious position.
This is the first evacuation called on a QF aircraft in living memory. The fact that it occurred at the worst possible time, at the gate after the doors had presumably been ordered disarmed, may go some way to explaining why it didn't go smoothly.
I also wouldn't mind betting that some stilletto heels has some role in the deflation of that slide.