Nope....
I disagree...
Small fire, from advise from tower, (the only way he could have known there was any fire at all),
You know the trucks are on their way....
Keep them on board, away from injury from the fast approaching trucks and subsequent flying foam etc, not to mention the 'certainty' of a small (not so small in this case!), percentage of the pax getting injured in the evac.
In the unlikely case that the progress of dealing with the fire does not go as expected, again as advised by the tower, then you can evac from the doors least effected from the fire or ground activities.
Portable stairs are much less liable to cause injury!