The entire POINT of “Hamilton” is to re-imagine the Founding Fathers as people of color in order to a) draw parallels between their struggle for liberty and the struggles of marginalized people today, and b) to emphasize that the story is vibrant and timely and relevant to everyone - it’s not just a story about “old white men.”
So consciously casting people of color is the roles is integral to the artistic vision of the piece - it’s using race to make a point. It’s not “discrimination.” And the role of King George is ALWAYS cast as white, and THAT’S specified in the breakdown too.
The only reason that particular notice got in trouble was the wording - you’re allowed to specify a CHARACTER’s race, but you’re not allowed to day that actors of a certain race can’t audition. So they fixed the wording.