The 1421 hypothesis is a fringe historical theory developed by Gavin Menzies, claiming China discovered the Americas seventy years before Europe. Emperor Zhu Di sent a fleet of ships (led by Zheng He) which discovered the Northeast Passage, Antarctica and everything in between. In the 1420s, a lightning strike burned down the newly consturcted Forbidden City which the administrators took as an omen which denounced the voyages. A year later, all new explorations were banned and evidence of them were ordered destroyed.
Menzies' theory is about as popular among historians as Creationism is around biologists. There is no real need to go into the details, but across the board they refer to it as "usless" and "without substance." So the question becomes "why." Menzies' made too many errors for his theory to be honest mistake. He might be trying to make a name for himself or creating more interest in his area of expertise. But I think he's also motivated by a hunger to downplay Europe's role in history.
In The Wealth and Poverty of Nations, David Landes argues the key reason why Europe developed faster than the rest of the world is because its people are free. Sure, other countries might stumble upon a new development but governments never allow people to expand on them. Terence Kealey echoes the same point in The Economic Laws of Scientific Research. While China had gunpowder centuries before Europe, it was Europe's free societies that developed the technology. Both works could easily be called "Eurocentric" (Landes is proud that his is) and be annoying to those who specialize in the history of the rest of the world.
There is good reason for Eurocentricism when discussing economic growth. Europe developed and continued to develop technology and trade as other parts of the world grew into stagnation. Any historical discussion of the underlying causes of economic growth must include the only success story. But this does not jive with the instinct for inclusion and fairness so people choose intellectual mediocrity. New ideas are great to have, but to quote Richard Dawkins, "You don't want to be so open-minded your brain falls out."