I'm not seeing the problem
They spotted something that looked like a possible weapon, carried by someone who looked like he could use it with deadly efficiency. They pulled him aside - didn't steal anything, didn't land their Millenium Falcon in his exogorth - he was in and out in five minutes.
While I haven't had any firsthand experience with the TSA {and the horror stories I hear make me avoid transferring via US, damn the plane costs}, this looks like exactly the kind of thing they - and any airport security, for that matter - is obligated to do. Keep eyes open, identify possible threats, investigate quickly, politely and professionally and if no threat exists, thank the passenger for their time and send them on their way.
Authority abuse is apparently commonplace in the TSA, but the knee-jerk reaction to jump down their throats whenever they do anything is counterproductive, IMO.