I'd never heard of this book (or theory before) but its Wikipedia page has lots of criticisms and claims that the book is basically nonsense (having said that, many of the references are to a site called 1421exposed.com so...¯\_(ツ)_/¯ ). The Wikipedia article about Zheng He's voyages (https://en.wikipedia.org/wiki/Treasure_voyages#Seventh_voyag...) has substantially better references and makes no claims (even speculations) that he ever traveled to the New World.

Let's just admit that if such a voyage did in fact take place, it did not make anywhere near the impact as in Europe.