As for the last picture, Sandra Laing felt so alienated by the Afrikaner community (even after the DNA tests proving her white father was her biological father, and despite being classified as White by law, she was still ridiculed and shunned) her only friends were the children of the black servants. She had no white friends, as none of the white kids wanted to have anything to do with her. IMAGINE you have the same blood as them, and they reject you, just because your mixed heritage is manifest, while theirs remains invisible! Nonetheless, she ended up marrying a black man, and even though her family OBVIOUSLY had African ancestry too, they shunned her and she was forever separated from her family.
Nonetheless, as for the level of African or Khosian ancestry in the Laing family, it had to have been somewhat significant, even though it did not show. While non-white admixture in Afrikaners is 5-7% and therefore negligible, that's just an average. Obviously just as you'll find Afrikaners with less than 5% non-white blood, you'll find some with MORE than 7% admixture. In Sandra Laing's case, her parents happened to be one of the latter. Even in the United States, where non-white blood is more negligible than amongst Afrikaners, there are a some white Americans with above negligible black ancestry. In the case of Sandra Laing's parents, the admixture had to come from BOTH SIDES of the family too. So both had to have had a total of at least 20% Khosian genes, in order for the meiosis to take place. A person who marries a partner with negligible to no non-white ancestry cannot produce a throwback. But if both have enough non-white ancestry on both sides, for meiosis to take place, a throw back is possible! This is the case with Sandra Laing's parents. Negligible non-white ancestry DOES NOT result in throw backs!
Nonetheless, the Laing case not only demonstrates that Afrikaners aren't pure, it also demonstrates that some Afrikaners have above negligible levels of non-white ancestry. And who knows, Arthur Kemp may be one of them! Both Sandra Laing's parents, state that on both sides of the family as far back as their great-grandparents, their family has been white. That still does not rule out the possibility that one of the great-grandparents (or some RECENT ancestor) was "passing", and that a whole bunch of individuals with significant admixture, just happen to enter the genepool! In Algeria where black admixture is very significant, an Algerian once said in one family you can get siblings by the same two parents (both showing completely Caucasoid features) in which a child is born with full-blown mixed Negroid features, while another sibling (by the same two parents) will be European looking and fair-skinned, whle still another sibling (still by the same two parents) is born with regular Berber features. He says since Mulatto types are considered a part of the "basic stock", such variation in a single family is considered "normal" and suprises nobody! The Afrikaners on the other hand, have NOT allowed mixed traits to be a part of their basic stock (even though they have high levels of non-white ancestry by European standards), which is why when the rare throw back occurs, they are taken by suprise! To a North African, there would be no suprise.