I wondered about that too. Then I realised they were talking weight not size.
I don't know how you would go about weighing a football pitch.

If it is any help I have the dimensions (Max and Min) of a football pitch but they only give the length of the vessel.
Anywhoo I reckon it is the length of about a football pitch based on:
The length of a pitch must be between 100 yards (90m) and 130 yards (120m) and the width not less than 50 yards (45m) and not more than 100 yards (90m).