At IAH and ORD this year, I have encountered similar set ups. You do the kiosk, then show your receipt, green card ( and passport, good god) to a passport control CBP officer. The customs officer only looked at the receipt.

At IAD this month it was like the original process when the program started; just hand the receipt to the customs CBP officer. I was somewhat surprised, and as ESpen did, walked slowly away from the kiosk with receipt visible, lest I get challenged. Lucky I did not have an X; there was no officer staffing the nearest passport control booth.