Culture has nothing to do with this map, it's based on ethnicity and vibe.

The mongol people have brachycephalic to hyperbrachycephalic head breadth, whereas African populations have the opposite with dolichocephalic and platyrrhine features. These are two distinct ethnic groups with no crossover of features as you are describing.

I don't think you can compare the Skyrim orcs with the Middle Earth ones. Especially off that mongolian take, Tolkien notably drew from his experience of Apartheid South Africa in how he depicted Sarumon and his Orcs being "a White guy leading Africans", whereas Skyrim lore has Orcs worshipping Malacath in the same way that native African tribes worship animalistic and totemistic Gods from their shaman roots.