If I read the OP correctly, the person was selected for Secondary BEFORE getting to the detector. And TSAMgr is correct - we're allowed to remain w/in view of our luggage at all times.
If the OP wanted to respond in kind to the TSA employee, could have cheerily said, oh it's not
my way, it's SOP for your organization. Thanks so much for following the correct procedure
Cheers. Sharon