I'm not an aviation professional, but I am a fireman, so I know a bit about fire. Been in quite a few too.
In the circumstances described, with the aircraft at the gate and the main door open, it seems to me that the most appropriate course of action, if the senior decided they needed to get everyone off the plane immediately, would be an emergency disembarkation via the main door. I haven't read the report yet, but I wonder why that option wasn't considered, or was rejected.
If conditions had deteriorated this could have been escalated to a full evacuation forthwith.
I'll say this much: as a firefighter, it would take a lot for me to criticise a... premature... evacuation. Yes it carries the risk of injuries, but I'd sooner have them off when it wasn't really necessary than not off soon enough; things can do downhill more rapidly than you would believe possible.
I'll leave discussion of the training, SOP, and CRM issues to the professional aviators!