I fail to see group hysteria, The writer did not show any hysteria on the plane. She was concerned of behavior that was consistent with terrrorists behavior. Also you can get an feel for a person based on a look. If you cannot read body language then you cannot percieve a lot of information from personal interaction.
If you feel this is all baloney, then perhaps you would feel comfortable being on that plane. Personally if I had to take a flight in the next 2 months, I would watch my fellow passengers carefully and if I saw more than a few middle eastern men, then I would refuse to go on that flight. If nothing happens fine, just an inconvienence to get another flight.
Maybe, maybe not.
In the situation she describes, I'd probably have innocently strolled over to the head (where they were "congregating") and struck up a conversation.
If they were hijackers, doing so would spook them or perhaps interrupt their plans. If not, then it would be nothing.
The notion of sitting there for 4 hours and getting more and more paranoid just seems ridiculous. That's no way to solve problems.