Why not? Don't you remember before the golden age of exploration in the 15th century, Europe was still under the gloomy shadows of the Dark Ages, where science and technology were being hindered from going forward? It was during this time where Eastern civilizations flourished and were in their heyday. Thus, it was impossible for Europeans to make voyages during this period, as many European countries were drawn into civil wars and their people were suffering from massive penury, famine and also the lethal Black Death. The Chinese Empire was already mighty and powerful during that time, and they had strong diplomatic relationships with many kingdoms scattered throughout Asia. On top of that, steamships aren't invented during that time. They only appeared on this planet in the late 17th century, which was 2 centuries apart. If you said that China couldn't have discovered the Americas due to its longer distance compared to Europe, then Australia couldn't have discovered by the British since Australia is far more distant from the United Kingdom compared to its Asian counterparts, right? A Venetian oil-painting which was painted during this period shows that a Chinese junk arrived at a Venetian port. This implies that the Chinese had succeeded in landing on the European soil even though the former and latter are far apart. Nothing's impossible, right? And as a Chinese, I truly hope that this truth is proven to be authentic.