This screams fraud to me. Even if Chinese mariners made it to the Pacific Coast of North America... this map shows the east coast of the Americas, too. How did the Chinese fleet uncover Antarctica and Australia? Why did the Chinese hide their knowledge of the Americas and Asia being separated by ocean when no one else in the world knew it until Vitus Bering? If this Chinese mariner did circumnavigate the world, he surely ran into other cultures - where are the stories from those cultures? A fleet of a 1,000 ships showing up in your local river would be enough to prompt generations of oral tradition. Where are all the artifacts left behind no doubt by sailors on a 1,000 ship fleet? The fleet brought home a giraffe to Beijing from Africa - why not a kangaroo, or a grizzly bear, or a narwhal? I say: PROBABLY FRAUD
That's a good one to start with. Then there's the "force" behind the beginnings of the great structures at Caholia. You betcha' a bunch of junks sailing up the Mississippi to St. Louis would have stirred 'em up. Hiawatha, the Great Law Giver, walked the Earth among the Iriquois. (These things are in the same time-fame.)