Dude could literally be writing in arabic "I wish this plane would blow up" and I'd still be fine with it.
We have lost our way as a free people.
THIS people.
The terrorists aren't stupid. We keep going apeshit about any form of dress that might vaguely be mistaken for Arabic and they'll simply make sure their men dress in standard western.
The vast majority of Muslims aren't terrorists, and we've expanded our hysteria to even include those who have nothing to do with them at all.
Keep in mind that
most attacks against planes today have been by non-Arabs. Local converts, mostly. That's going by recent history. They still haven't reached the point of communist wannabes taking planes to Cuba back when I was a kid.
I have to wonder what the response would be if the lady saw the guy reading a gun magazine and raised concerns about him having a gun on the plane.
Probably about the same.
I don't really care what people wish for. If he's listing off the ways he saw to get a bomb past the security checkpoint, or writing out his will I'd at least want to have someone watching him.
Why? If he's cataloging the ways to get a bomb past security that he saw, that means that the bomb isn't on this flight, and your attention will probably just amount to harassing a legit security researcher. Like what happened at a Canadian University semi-recently. Guy was doing a report on anti-terrorism efforts for his college anti-terrorism class and that wasn't considered sufficient for the local po-po who had to close down the library for a bomb search(negative) and question him for several hours despite the dude being able to show registration for said class, the assignment, etc...