The manager could have called the toll free number on the back of the card to get the total amount left on the card but then that would not have been very fair to the other customers I am assuming were waiting since it was lunch time.

Is there a different machine other than the credit card one that they use? Maybe I am being a bit ignorant since I never use credit cards, but when I use my Subway gift cards it looks as if its swiped thru the same machine as the gift cards...but again I may be wrong.