It looks like there will be a dedicated line for mobile passport. I'm guessing they were piloting various things, including the kiosks which are not ubiquitous.
http://mobilepassport.us/
STEP 4:
SKIP THE LINE & SAVE TIME!
Follow the MOBILE PASSPORT CONTROL signs and skip the lines! Show your passport to the CBP officer and scan the barcode on the CBP receipt. And that’s it!