When to call an evacuation is only the captain,s decision SOP is for advice only..
ie consider immediate evacuation If a specific threat still exists
Consideration includes the threat and consequences for a delay in disembarking for minutes and possibly hours.
The decision to return to departure airport and fuel jettison
is not made lightly. Only done for a very serious threat.
The bomb was visible and the threat to "blow up this plane". ,was not a hoax but made by an attempted hijacker.
I would be very wrong and dangerous to assume the bomb was not real and possibly filled with high explosives packed with ball bearings etc.
* I don't think it wise to assume zero damage threat
The police and various bodies are now in control.
This is not correct.
The captain is total control until the engines are shut down.