Two engines running, albeit with one at idle, is not an emergency condition.
Every aircraft type (a technical term) I’ve ever flown, the abnormal checklist for an engine vibration called for a reduction in power. If the vibration went away, the engine remained running - it kept extra electric, air, and hydraulic systems available. The pilots were highly trained to make a normal landing in this configuration.
As to the “evacuation”, I highly doubt it was an ordered evacuation. I suspect a passenger decided on their own to pop the exit. Otherwise all of the other exits except the right overwing exits and the main cabin door would have been opened with chutes deployed.
I’m waiting for more info.
EC
the reply was in reference to the statement that the pilot must declare the emergency. the answer is that anyone in that ATCT can activate the crash phone and roll the emergency vehicles. Let the crash captain sort it