This isn't really all that uncommon. The first time I read about it was the late 1970s, in that case the mother was "black" and the twins were still babies.
The doctor's account of the genetics in the article is wrong, also. There are at least 5 different genes affecting skin color which show mixed dominance with darker being dominant. So a "black" person with a single white ancestor many generations ago can still carry the genes for light skin as a recessive; which can be expressed in their children given the right mix of other genes. Hair texture and color are similar, I don't know about other characteristics. The only reason I know as much as I do about the skin color genetics is that they were used as an example for tracking complex, multigene inheritance over generations in a human genetics textbook I read in the early 1980s (I have not even the vaguest memory of its exact title and authors).
The doctor's account of the genetics in the article is wrong, also. There are at least 5 different genes affecting skin color which show mixed dominance with darker being dominant. So a "black" person with a single white ancestor many generations ago can still carry the genes for light skin as a recessive; which can be expressed in their children given the right mix of other genes. Hair texture and color are similar, I don't know about other characteristics. The only reason I know as much as I do about the skin color genetics is that they were used as an example for tracking complex, multigene inheritance over generations in a human genetics textbook I read in the early 1980s (I have not even the vaguest memory of its exact title and authors).