Unnecessary delay
Strongly disagree that the delay in evactuation was necessary or satisfactory. Read about the BA 737 accident at Manchester (UK) in the mid 80s (56 fatalities, from memory).
If it's a serious fire every single second counts. From the cockpit, you can't tell what's happening in the cabin - whether there's fire visible outside or not, how fast it's spreading. So you have to assume any reported fire is serious.
If someone you trust tells you that your aircraft is on fire on the ground, stop it and evacuate immediately. Think about your heading relative to the wind and the position of the fire, if known (in the Manchester accident they stopped in a position where flames from the burning fuel prevented use of at least one of the exits). I don't believe anyone on board an aircraft is in a position to make an educated judgement about the severity of a fire, and then use that judgement to delay evacuation on the ground.
I don't for one second believe that it takes several minutes to run the checklist for this occurrence.
I don't have any special knowledge of this incident, so I can't comment on what the causes for a delay might have been. Conceivably it may not be the pilots' fault.
I'm not a firefighter; but I've received a reasonable amount of firefighting training (for work in the offshore oil and gas industry). I've also been on platfroms/rigs where fires have broken out, and seen how quickly the situation goes from 'under control' to 'f**d up beyond belief'. If the delay in evactuation was elective, the situation wasn't being taken seriously enough.
Lucky this time...