Commercial Aircraft at Moffett Field

Last week, while driving into work, I saw a rather unusual sight. An AirTran airliner was taxiing at Moffett. It looked like it had just landed. Why was it there? Did NASA buy the aircraft, and it simply wasn’t repainted yet? Was it an emergency landing, and if so, why not just land at Mineta which is just like five minutes further south? Was it some sort of bizzare mistake?

Googling around, I found the flight: AirTran 8141 from Halsey Field San Diego to Moffett. Halsey is NAS North Island, so it was flight from one government airport to another, but still seems a bit unusual for it be a commercial flight.