How is Brock the only Asian character. I always thought he was black
Doesnt the show take place in a fictional part of japan
Yes, for the most part.
Appearances in anime aren't usually directly linked to nationality or race, as everybody in Japan is Japanese and so by default everyone on television is Japanese (or European if it's a fantasy setting). It's usually used to convey character traits if anything.
Monster and FMA B are the only two anime I can think of that do distinguish between races and discuss race as a topic, though I'm sure there are more. For the most part Japanese people don't really view race as a topic because its never been a topical issue in their country (which is not to say that Japan can't be or isn't racist).