Cabin crew may initiate an evac in 'catastrophic' events. Depends what their view of catastrophic (in our SEP training course there is no verbal definition, just a picture of an aircraft in pieces with flames coming out of it, with a cartoon pilot looking very unhappy!) is but to them fire is fire. We don't know the full extent of the interaction (or not) between the cabin crew and the flight crew but as a general rule you can be sure the cabin crew would be able to justify their actions in a situation as serious as an evac. Their job is to ensure the safety of all the people on the aircraft.