They're profiling people looking for anyone that is too nervous/properly engaged with the event/etc., so he got targeted. And as usual the profiling got a bit out-of-hand.
That reminds me of an old joke(I try to use those in the Public Domain(tm) since I can't afford royalties)
Back when the hijackings of American flights were usually to divert the plane to Cuba, they came up with Sky Marshals to counter the threat. These were non-uniformed law enforcement types on the lookout for suspicious passengers.
The joke goes that due to an administrative error, two Sky Marshals were assigned to the same flight. They reported each other to the Stewardess(as they were called back in the 60s) as the most suspicious passenger on board.
(I think Archie Bunker had a simpler solution. Instead of all the bureaucratic red tape just have someone pass out pistols to the passengers as they get on board, and another guy collect them at the destination.)