Regular sources as in MSNBC, CNN, NPR, Wikipedia, etc. sources that are the most established, enough that they’re among the top 500 websites and that they show up on the first page of a Google search. Not to mention a random source is going to have random origins, trust in a source has to be earned and even with trusted sources you must compare and contrast them sometimes.
The restrictions for leaving and entering have not been imposed on them externally, this attitude of Korea predates even the Roman empire so external factors wouldn’t have been possible as a cause, even though it’s undeniable there are nations that have restricted anyone from going there. Japan used to be the same way at different points in history, though for the time being they’re open to everyone.