One of the two aircraft commonly known as "Air Force One," even though Air Force One is really any air force vehicle that the President is currently in, flew over New York City, without the President on it, accompanied by an Air Force fighter jet(s) in order to take a picture of the aircraft with the Statue of Liberty in the background.

Because this was not widely known about at the time (the Mayor of New York didn't even know about it), it frightened many of the civilians of New York, as they were worried about another terrorist strike that had occurred or a hijacking of this aircraft. Because of this disturbance, people got mad, and needed someone to blame for all of the people getting worked up. As Obama is the figurehead of government, he was who everyone looked to. And he says that he didn't know about it, and many people disagree.

That is what they say he is lying about.