You don't screw up something this major, it doesn't happen by accident nor by incompetence.
They had plans to bomb something south of that airport, they had to postpone those plans now that the info is public enough that whatever their target was is definitely aware of those plans.
> You don't screw up something this major
Liz Truss begs to differ.
This is exactly what happened and not to be immodest but it was my first guess before it was confirmed. The closure was a miscommunication between the FAA and Pentagon set off by a balloon. This was pure incompetence and arrogance. This HN thread is almost unbelievable how many wild guesses were made.
https://www.cbsnews.com/news/airspace-closure-followed-spat-...
They have confirmed it was for testing a counter-drone weapon. They did not say why they set it to expire in 10 days, that part seems like it was probably a mistake.