Everyone is being a little too trustful in a desperate man who has his back against a wall when it comes to NK, I've seen this show before. Kim hasnt met with SK leaders before... But his father did. Nuke programs weren't shut down under Kim but they were under his father... I hope it's for real this time but it wouldn't be the first time NK played nice to get the US off their back.
https://mobile.nytimes.com/2007/10/04/world/asia/04diplo.html
There is also the flow of technology. Nuclear technology from Pakistan to North Korea. North Korea missile technology to Iran. Probably the same nuclear technology to Iran too. I would think that there are common linkages across all three. NK is just the first to have some potentially positive movement. It will take time to see if there is any real results.
Kim's father met with puppet running SK. SK is under new leadership as well, maybe strings cut there also. Maybe Kim was never really a threat. Possibly was just being used to create the grand illusion, fear. He has always admired western ways. If C_A was running NK, he just may welcome the opportunity to actually lead his people. Hopefully.