How did Kun Yuan explain it?

"Kun Yuan" is not a disyllabic word, but a phrase, that is, "Kun" is an adverbial of "Yuan", forming an adverbial phrase. These include:

Kun: noun, Shuo Wen: the divination of Kun, Di and Yi. It means "Earth". Far: adjective, Shuo Wen is far away, and Liao is also. That means "far away"

So the general idea of Kun Yuan is: The earth is far away.