And as historians, both and Polish and not pointed out at the time, the argument that it's Medieval Poland rings incredibly hollow as it's very likely Poland was more diverse then it is now thanks the extensive trading it had with nations from the east, Poland was not self-sufficient, little to no to Europe and because of it's geographical location, Poland was a hot spot for trading which when you are a nation in constant threat and attack from Western Europe, good trade and resources was essential. What CDPR basically did was the "their was no black in Europe!" BS you see on the web all the time.
Plus their is the fact that no much of the Witcher is actually based on Slavic mythology, it in fact borrows heavily from German, Norse, Greek, Arabian and many other mythologies (which is kind of a shame because Slavic Dragons are really interesting and would have made cool monsters to fight against). This is because sadly quite a fair bit of Slavic folklore and mythology was purged or altered when Christianity took over and tried to suppress it.
Edit: Wow, it's really disturbing how many commenters here really do believe in the BS "their were no black people in Europe" falsehood... Like yikes, it's really really not true and only a thing because of how warped our perception of medieval is because of the media and osmosis, I seriously recommend people to look and research POC in Europe first before commenting because seriously not a good look at all and really makes believe that 4Chan and the racist side of the web have succeeded.