It is really beyond silly.

Doesn't Mr. Williams realize that others have also noted the presence of 'Muslim-garbed' people? Does the presence of an Indian woman with the black dot on her forehead make him uneasy? Does a cowboy in chaps and spurs and tall hat bother his sensibilities? (Well, yes) Does a clown dressed to entertain at a children's party upset him? Does an Amishman in 'plain' clothing make him want to reconsider his flight? Does a robed Muslim family that has passed through the security gates scare him? I guess so.

As implied above, if you want to commit some horrendous act you don't want to attract attention beforehand.