From what little I know about using ginger, that should be 2.5oz. Papazian says you should use fresh, grated ginger. He says 1oz will add considerable character, but that he's used as much a 4oz in a batch.
The 40oz was NOT a typo. Keep reading into the thread. Fresh grated ginger has a some heat and some more subtle gingery flavors. Boiling the ginger which this guy did, removes the heat but leaves the subtler flavors.