There are probably layers of government here, and this is the first stage of the basic truth bubbling to the surface. If there is no national security threat, the Air Force, or government as a whole, doesn't ultimately need to concern itself with investigation. Blue Book established this in the 60s.
So why keep it classified? Russia, or more accurately the Soviet Union. The US needs to keep what it knows classified in order to maintain an edge on Russian technological development.
Soft disclosure can take place, like this, without jeopardizing the technological advantages being processed at the deeper levels of government. Tom Delonge's group can be the pressure valve allowing general information to come forward. Finally.
In short, they're real and they're not a threat, but everything known about their technology can't be released so some secrecy is required.