The quote of Major James Fox saying, "I've never seen so much real-world stuff happen during an exercise" is really suspicious. I wonder if the staff at NEADS understood "real-world" to mean a live-fly field training exercise, as opposed to a purely simulated command post exercise?
So when Sgt. Jeremy Powell asked Boston flight control center "Is this real-world or exercise?" he could have been asking if the exercise was live-fly or not. And when Boston replied "this is not an exercise, not a test," he took it to mean that it was indeed a live-fly exercise, involving a plane under the control of the military pretending to be hijacked.
This would certainly explain the bizarre conversation between the NEADS "ID techs"—Stacia Rountree, Shelley Watson, and Maureen Dooley—when they heard of the reported hijacking:
8:37:56
WATSON: What?
DOOLEY: Whoa!
WATSON: What was that?
ROUNTREE: Is that real-world?
DOOLEY: Real-world hijack.
WATSON: Cool!
I find it hard to believe Shelley Watson would have responded,
"Cool!" if she thought "Real-world hijack" did really mean a genuine hijacking. Might she instead have believed it to have meant a "live-fly," with a real plane pretending to be hijacked, for which they could launch fighers in response?