This story has been on WorldofCoins recently, too - it looks like the story is two years old and is being repackaged. The coin isn't rare, either - the Yongle coins were very popular throughout South-East Asia and were widely copied.

The "Yongle" (read as Yung Lo by the Japanese) coin was also extensively replicated by the Japanese as a trade coin for a long time, so the visitors to Kenya were not necessarily Chinese. They could have been Dutchmen returning from Dejima. For that matter, they could have been Portuguese as well, returning from China or anywhere in southeast Asia.

There are several references published decades ago about finding cash-style coins in East Africa. There was a huge Chinese fleet that sailed from China and went around the Indian Ocean. They even carried some Vietnamese cash-style coins (one of my specialties) and they have been found mixed in with large quantities of the Chinese coins. I seem to remember it was a one-time trading and exploration trip for the Chinese and not a regular "trading" visit. But it would not be unreasonable for other traders from Africa, Middle East and South Asia to be carrying cash-style coins on later journeys and use the cash-style coins to trade for other goods.