It turns out these viewers were correct. The footage used was not only outdated, it also wasn't all even footage of Jacksonville.
The AFC South Blog on ESPN.com published a statement by an ESPN spokesperson about the error.
The Charlotte aerial was an inadvertent mistake. It should not have aired. We apologize that it was part of the telecast. The scenics of Jacksonville that were used during 'Monday Night Countdown' were shot the night of the previous MNF game there in late October. We did not have a crew shooting scenics Monday. There were no graphic or audio mentions indicating the shot was live, though we understand viewers may have been under this assumption.
The statement only provides us with more questions than answers. Since when do TV stations use old footage of cities during games? Why didn't ESPN bother to have a crew take shots of Jacksonville? And when and where exactly did the footage of the UFO sighting that wasn't actually a UFO sighting in New Orleans take place?
(Hat tip to Sports Grid for the video)