Dutch newspapers in fact confirmed that is WAS a practice fire drill, and there was no real fire.
They also reported 'What is it that can’t be simulated with running from a building', Knold, it's that they have to move to the emergency tower to resume operations. Obviously leaving a skeleton crew to continue operations would defy the object of such a drill.
The newspapers also reported the max delay to aircraft was only about 3 minutes, something which isn't true then according to Few Cloudy.
All in all, I think the exercise is worthwhile to train controllers to leave their desks for a few minutes to continue in the backup tower. It seems difficult to me, and it's not practisable in the sim.