Without knowing a lot more, it's hard to place a lot of blame on the FAs. The break might have been their only chance to get food at a reasonable time, and it's not necessarily their fault that they were suddenly assigned to another flight when they were otherwise expecting to eat lunch.
As you point out, it seems like the kind of problem that American could probably solve by having someone to get them from point A to point B and possibly providing lunch so they could start to get ready for the flight without waiting in line at McDonalds.