I doubt AA fake a mechanical on this one, but there are still grey areas. You know that if one of CO's 777 for EWR-LGW have a mechanical, and that both flights are like 85% full, they will do everything possible to fix the plane and get the flight out, and CO usually has one or two 777s at EWR for standby.

But AA may take a less urgent stand, as channa has explained clearly why.