u/aimixin - originally from r/GenZhou
There is not a single source for any of these outlandish claims. Just a person making stuff up to get upvotes on reddit, and others upvoting it because it supports their preconceptions. That which is presented without evidence can be dismissed without evidence.

We do not assert that the Koreans' biological constitution is more developed than those of other races. Defining the superiority of a nation according to biological or ethnic characteristics is the practice of reactionary, bourgeois ethnology. Arguing that national characteristics are defined by racial characteristics, bourgeois ethnologists classify people according to skin colours, namely white people as a “higher race" and coloured people as a “lower race”. They say that only a “higher race” can create advanced civilization. The reactionary ethnological doctrine has been used by imperialists as an ideological instrument for their policy of racial discrimination and obliteration of nations. Imperialists still use the bourgeois ethnological doctrine as an instrument to justify their domination over other nations, to spread national nihilism, the idea of subservience to great powers and the idea of dependence on foreign forces among the people of colonial, dependent countries and the people of the third world, and to obstruct their national independence and independent development. Fundamentally speaking, there can be no “higher race" or “lower race”. All the races are endowed with creative intelligence and ability. The low level of civilization of nations under colonial subjugation in the past is not due to any inborn inability, but is the consequence of the imperialists' predatory policy and their policy of keeping colonial people in ignorance. The people of the third world, who were despised by the imperialists as a "lower race", have now become the masters of their destiny, are making brilliant successes in the creation of a new life and are steadily raising the level of their civilization.

--- Kim Jong-il