There have been previous reports of USA destination passengers asked to present a second form of ID, there was a report of CDG doing this a few months back. I can only speculate but it may be when the interface with the DHS goes down that the ground staff come up with this made up rule to cover themselves in case of any adverse cases picked up by the CBP on arrival. My second piece of speculation is that some other airline may have this requirement and because ground agents move daily between airlines they sometimes get mixed up as to which set of rules apply. It is not a BA requirement, we know that.