No, because sometimes they need a plausible excuse to act on other suspicions.
When working security, agents can sense something is wrong but not have it articulable enough in legal terms to act on. When the suspect says "why are you searching me?" it's a lot easier on everyone to say "the detector beeped, you heard it" than "I've got an uneasy feeling about you". (Not legal, not warranted, just easier.)
I'm pretty sure they don't need any excuse at all. They can just do a "random" screening - which is designed exactly for that.
The only reason to keep screening him over and over is if the detector really did find something, otherwise they are just wasting their own time because of a nebulous feeling.
Uh... The person has already exhibited enough suspicious behavior and circumstantial evidence to get frisked & questioned in a back room and their ticket cancelled. Indications are this is the kind of person being looked for, and if is, at this point is trying very hard to not reveal any further evidence of ill intent. Time to crack the egg and see if it's rotten.
When working security, agents can sense something is wrong but not have it articulable enough in legal terms to act on. When the suspect says "why are you searching me?" it's a lot easier on everyone to say "the detector beeped, you heard it" than "I've got an uneasy feeling about you". (Not legal, not warranted, just easier.)