I had a similar experience at ORD in May. A CBP officer was stationed in a booth past the GE kiosks and was asking those with GE receipts a couple of questions each. I was just asked where I was coming from (TPE via NRT) and purpose of travel (visiting in-laws) and sent on my way.

Perhaps it's to check and clear you if you get the X. My guess is that people might have been thinking that meant handing the form to the officer while leaving the customs hall. Most of my GE use has been at DFW or LAX (TBIT), and there is really no convenient path and you have to swim upstream if you get the X and have to report to passport control.