Technically, an Air Force plane is not "Air Force One" unless POTUS (and presumably, TOTUS) is on board. At all other times, it goes by its normal identifier.
The other branches of the armed forces use the same convention. For instance, "Marine One" is the helicopter that lands on the lawn of the White House -- but only when the President is on board.
Reportedly, "Cadillac One" is the nickname of the armored limousine.
I’m saying they’re lying
Obama’s lying is Clintonian. Air Force One with the President on board could be described as, “A 747 used as Air Force One.” No where in the article does it imply that it wasn’t AFO at the time. Even if it wasn’t, who did he give the keys to, Michelle?