Your forgot to include the next line, which may provide a key to why this claim is being made:

And that is profoundly influencing the way Kenya is thinking about its current ties to the East.

When the re-writing of history is accompanied by a particular political push, it should raise red flags.  Using history as a tool to further present-day politics is what we should be suspicious of because we know that the person doing the re-writing has a “dog in the fight”.Now, that's not to say that history cannot be re-written and thereby bolster a political argument or group.  It's just that it merits special scrutiny.More immediately, if we look at what the article says, how much can we learn from the presence of one coin in Kenya?  Even if they were only carried by envoys of the Chinese emperor, they're still highly portable and transferable.  How do we know if didn't eventually make its way into the hands of some European merchant in the late 17th century before arriving in Kenya?  Too much speculation here to provide any real useful conclusions.