Lets say there is a bomb. And it has a phone attached. And you have inside information that it is really connected to a real cell phone. And you don't know where the person is with the other phone. And you know from your inside information that the timer will wait 6 hours before the fail-safe makes it blow up.
What if it is not a bomb. What if a war breaks out, and you know for a fact that there is an intelligence agent reporting over a regular cell phone, using coded words, about the movements of ships out of a harbor. Cutting off that flow of information while you set sail might be very valuable.
I'm not arguing for (or against) the wisdom of these policies. But there are obvious and legit reasons for the government to make plans for how to deal with unlikely emergencies.
They probably also have plans for what to do if we're invaded by Canada. Not because it is likely, but because a nation this large can afford to plan for unlikely things. Some of those unlikely things will actually happen.
As to this case, the Executive gets to tell the Court that their reason is that their conclusion is that National Security requires it. That it is their opinion makes it a good enough reason, because national security is not the business of the Court. Expect this story to be nothing, and go nowhere. For or against the policy, you should be able to see this approach will not yield any fruit.