My assumption at this stage would be that the North Koreans are banking on Trump's eagerness to be seen as the great Korean peace-maker. They're getting in some preliminaries though, so they won't be seen as weak. No, we're not giving up on our nuclear weapons, and yes, we hate John Bolton - "We do not hide our feeling of repugnance towards him". Get rid of him and there might be some chance of progress.
As far as Pyongyang is concerned, they'd like us to believe that the forthcoming US summit is no big deal. They've already made their point. Kim is now established as an accepted and respected world leader, and North Korea is an acknowledged nuclear power, with all the prestige that that bestows. Presumably, after those friendly meetings with President Xi, they feel they have China's backing.
The ball is now in Trump's court.