There are (contingency) plans in place for strikes.
You have two groups of people. You have everyone who was scheduled to go out today and everyone who was scheduled to go out yesterday, trying to rebook today.
It was not a bomb threat, he did not have a weapon, he did not say he had a weapon, he did not say he was going to blow up a plane or anything. But the nature of the wording was enough for them to decide to take the action they did.
I walked around last night and there wasn't 20 people here.