I’m not so sure but i don’t think that could be the case tbh. Despite being seclusive country, they do allow student to study abroad and they allow their people to work abroad as well. Under what condition, i don’t know, but the number is very limited and they also allowed back in for “reeducation”. This article has a tiny bit of info on this. I suspect they made use of social alienation so even when they went back and tell others what’s it like, no one will believe it because of how deep the indoctrination run.

Edit: to add, these are the top soldiers they sending, NK will definitely want them back.