All base operations are classified the moment they happen. Obviously, you have no experience with the military. I spent over twenty years on submarines. Every operation we did was considered classified. Some of it was considered just operational security and some of it was very classified. Anything concerning the engine room was classified at least "confidential". I am sure the AF classified most air operations at some level to ensure that details about them could not be well understood by other countries.

Of course, this brings up the greatest question. If the event was classified to hide the truth about "UFOs", why wasn't it classified to the point that it could not be released via FOIA? This can be done you know. Instead the AF simply released all they had on the case because, to them, it was worthless. To UFO groups it is a godsend and they can portray the event as they want to, including the fact that it was "classified" and kept from the public for many decades until a group of diehard investigators found the truth. How gullible can you be?