Meh. Passenger demonstrates willingness to a) revisit the incident later and b) use the word 'terrorist' on the plane.
They don't have to actually think he'll blow up the plane; it only takes one closet nut case to overhear this and cause a ruckus mid flight. In a small confined space at 30k feet that's a very real safety issue. Consider that an irrational fear of flying isn't that uncommon, and this is a route where there isn't much of an alternative.
Finally, they're under no obligation to tell a passenger the real reason for booting him off the plane; if it was the above, doing so could only make it worse for themselves.
So not only <xyz protection racket comparisons>, you can't actually even bank on it if you get it. '[..] says he's gotten Precheck screening on about 80% of his trips so far [..]'
While I'd much rather sit in some miserable lobby than stand in line for two hours, this means you save exactly zero time unless you're happy to miss X% of your flights..
They don't have to actually think he'll blow up the plane; it only takes one closet nut case to overhear this and cause a ruckus mid flight. In a small confined space at 30k feet that's a very real safety issue. Consider that an irrational fear of flying isn't that uncommon, and this is a route where there isn't much of an alternative.
Finally, they're under no obligation to tell a passenger the real reason for booting him off the plane; if it was the above, doing so could only make it worse for themselves.