Well, the feds are trying to pass it off as an airliner. Odd, the only ones who have said that are the Pentagon and NASA. No way that THEY would have any motivation for giving that explanation...
My take: Somebody royally screwed up, and now the Pentagon is trying to cover its hindquarters. I've seen a LOT of planes flying - jet fighters, passenger planes, etc. That is either a missile or a small space launch.