The guy in the video is arguing "Chinese and Japanese" people have it due to their ancestors being involved in incest.
Black Israelites, Five Percenters, and a host of other smart-dumb negros use etymology to explain any and everything, and thus make leaps in logic that truly baffle the sane mind. The use of the word "mongoloid" and its origin has no bearing on the genetic history of Asian people. Likewise, the word "black" (which they claim is offensive) has no true bearing on the genetic nature of black people, their worth, etc. On one hand they argue the white man has poisoned the world with misinformation, on the other hand they use that very misinformation to somehow validate their arguments.
The western concept of "black" is completely different from the ancient African concept of it. "Black" was associated with power and beauty in ancient Egypt and other African nations, whereas the color white was associated with death or "the absence of life/light." It makes sense that a civilization would associate its racial traits or color with "good" - western culture does the exact same thing, with the color white being associated with purity, goodness, etc. And because we live in a society dominated by western, white culture it shouldn't be surprising that those are mainstream views.