I suspect that the head of state in Seoul, and the US president colluded to have Trump play the saber rattling " bad cop", and South Korea play the "good cop". Seems to have worked to bring the two Koreas into a conversation.
In the short run in might do some good.
Some nations have discontinued nuclear arms programs. But no nation has given up nukes once it crossed the threshold of actually getting nukes. Would Kim Jong In be the first head of state to give up nukes? Not impossible. He seems to have built them for two reasons: to get attention, and to prevent us from doing a Bush-Cheney regime change on him. He has now gotten the attention. And he will always have his neighbors the Chinese to step in if we invade his country. So conceivably he might actually give up his nukes. But he would ask a lot in return. Some kind of aid package in food, or electricity, to stave off the collapse of north Korean society.