Join Date: Jul 2002
Location: Still going through ORD security when boarding has already started
Programs: AA EXP, UA Silver, HH Gold, Bonvoy Gold, IHG Plat, Hyatt Disco, Reno Air MEGA Platinum
Posts: 10,289
It's possible the OP had the first leg of the trip on UA metal connecting to a US flight. Therefore when checking the bags, the OP would have checked in at a UA counter. I don't see any other way it would work....