This has nothing to do with real borders, but with the distance to the nearest capital (that's how Voronoi diagrams work)
For instance, that shows that more than half of Russia territory is closest to the capital of Mongolia (which is Ulaanbaatar) than to Moscow, that's the point.
For instance, that shows that more than half of Russia territory is closest to the capital of Mongolia (which is Ulaanbaatar) than to Moscow, that's the point.