I assume that the absence of Tibet is related to transitivity, in that Tibet is currently controlled by China so on a map that indicates current borders, it would be inside of China, which was partially controlled by Europe.
That also accounts for the grouping of the Koreas with Japan. Korea was a colony of Japan, which was never colonized by Europe, so gets the same color as japan.
I assume that the absence of Tibet is related to transitivity, in that Tibet is currently controlled by China so on a map that indicates current borders, it would be inside of China, which was partially controlled by Europe.
That also accounts for the grouping of the Koreas with Japan. Korea was a colony of Japan, which was never colonized by Europe, so gets the same color as japan.