I really don't see a big deal here. The books are set in a fictional world where history of racial migration doesn't have to mirror ours. Why does it bother people so much or "make no sense" for a character's race to be different? It's a different medium so having a new twist on an existing property is more entertaining than seeing the same old thing.
On the opposite spectrum, we have a bunch of people who went crazy over The Ghost in the Shell live action move casting Scarlet Johansson as the main character. I agree that there aren't many lead roles for minorities so including a diverse cast isn't a bad thing. However, I don't believe this was a case of white washing. News flash, the character in the anime has BLUE eyes. When do you see Asians with blue eyes? Of course, you can chalk that up to the shell having blue eyes, but then again, if you went with that reasoning, you could apply that logic to her entire shell's Caucasian appearance. Her ghost may have been Asian, but her shell was off the shelf white (just like the movie). Makes sense.