SFO "reason for opt out"

The past two times I've flown out of SFO Terminal 1, I've been asked the reason for my opt-out. The first time, in early November, I asked if I was required to give an answer, and the agent said no. No big deal, but it definitely felt less "customer satisfaction survey" and more "intimidation tactic."

Yesterday, I was again asked the reason for my opt-out. I asked whether I could decline to answer. The agent said "Oh, sure... you can decline to answer... and then I'll send you right back over there while I call over a supervisor."

Is this a new thing the TSA are doing in an attempt to discourage opt-outs? If it's a voluntary question, then why was I threatened with detainment for refusing to answer? I don't read the TSA blog, I just notice things getting a little bit more ridiculous every time I fly.