Marx explicitly wrote that a Communist country would be ruled by the worker. And since the only people left after a Communist revolution would be workers, it would be direct democracy (scary **** eh?). Due to there only be workers, there would be a classless society. North Korea fails those two criteria right off the bat.
Moreso, Marx wrote that a Communist nation does not trade with the West. North Korea at least matches this partially, but not by choice. For the same reason China and the Former USSR fail this test (and the earlier two, gang of 6 anyone, worker rule my ***?). And more importantly, Marx wrote against Capitalism and property rights. China and Russia have brought those back with some caveats, and North Korea has property rights for its elite class.
If we stick with the actual definition of Communism, North Korea fails pretty hard in almost all categories. The problem with defining Communism based on the actions of those in the past 50 years is that it renders Communism to mean whatever self proclaimed Communists have done. Which include strong property rights, a ruling elite with little to no voice by the people, export oriented economies focusing on the West and frameworks to encourage capitalism. The idiotic idea of defining Communism not by what Marx wrote but by what "communists" have done is that it renders most countries in the world at some point in their history Communist. Is that intelligent? No. Does that produce any thing of value? No. So why do some people use it? Probably because they first don't know what Communism actually is and don't realize they just classified Switzerland as Communist.