I also got to know Jeju because of the same reason
The USA is much closer to Havana than it is to Mexico City...
Now I know the term doesn't fit South Korea anymore, but North Korea is also not really known as the "Hermit Kingdom"
Both is most correct, but actually, both are no longer known as the hermit kingdom.
The question makes sense towards the current countries with regards to North Koreas isolationist policies.