For whatsoever man he be that hath a blemish, he shall not approach: a blind man, or a lame, or he that hath a flat nose, or any thing superfluous, 19Or a man that is brokenfooted, or brokenhanded, 20Or crookbackt, or a dwarf, or that hath a blemish in his eye, or be scurvy, or scabbed, or hath his stones broken; 21No man that hath a blemish of the seed of Aaron the priest shall come nigh to offer the offerings of the LORD made by fire: he hath a blemish; he shall not come nigh to offer the bread of his God.
Leviticus 21:18-21
I do not believe it has anything to do with race. As you can see, many of the blemishes are not from birth but from wounds in war, accidents, etc.
Deuteronomy 23:1 He that is wounded in the stones, or hath his privy member cut off, shall not enter into the congregation of the LORD.
From this context, I would have to say that a flat nose is one that has been broken.
(King James had no part in the actual translating of the Bible known by his name.)