The (Alleged) Ostrich-Egg Globe of 1504

This is said to be the oldest globe that depicts the New World. Carved on an ostrich egg, it shows a fairly convincing South America but just a few islands for North America. Its date is said to be 1504, based on a recent analysis. Since Balboa is generally said to have been the first European to see the eastern Pacific, in 1513, I wonder how anybody in Europe knew that Panama was only a narrow isthmus in 1504.