Just looking at that map, I'm a little skeptical. If that is supposed to be a copy of the map drawn by a Chinese sailor who crossed the Pacific, how did he get the east coast of Central America to be somewhat correct, not to mention the St. Lawrence? Are they claiming that he crossed the Americas overland, or sailed around Cape Horn?
Otherwise you need to imagine exceedingly large Chinese ships navigating the Straits of Magellan.
"I'm a little skeptical."
Yeah - all the rivers - esp the ones in Alaska and Siberia - they must of had jet boats and lots of fuel to explore them ... and how did they miss the Amazon?