Al-Madadi, possibly offended that this puny non-diplomat insisted on talking to him, answered with a blank stare and responded that he had, in fact, been trying to light his shoes on fire. Unfazed, the flight attendant asked al-Madadi for his lighter, which he of course refused.
So, let's recap: A suspiciously behaving man exits a bathroom that omits a strange smoke, makes a direct reference to Richard Reid's post 9/11 shoe-bombing attempt and refuses to cooperate with the staff. On a plane.
From that point, things escalated like the world's strangest Benny Hill sketch. The plane's U.S. marshals were called over to calm al-Madadi down. They grabbed him, put him in his seat and, while keeping an eye on him, alerted the pilot of the situation. The pilot, in turn, kicked things up a notch by sending out a "potential terrorist" status report, which led to the usual motions for this kind of situation, including sending out fighter jets and actually alerting President Obama about a terrorist scenario. You know, usual diplomat stuff.
Al-Madadi's ass was detained the second the plane landed, which is when it was found that he was, no s**t, on his way to meet with a terrorist who was implicated in 9/11.