Something I've noticed at these Moon-Kim summits is how Kim Jong-un downplays the development of North Korea. It's quite a change from trying to put on a facade (like his predecessors would) to being candid and frank about the situation.
At the first Moon-Kim summit, Kim Jong-un said "I feel embarrassed about the poor transit infrastructure" according to the BBC.
At the third Moon-Kim summit, Kim Jong-un said "You Mr. President are travelling all around the world, but our country is humble compared with developed nations. I’ve been waiting and waiting for today. The level of the accommodation and schedule we provide may be low, but it’s our best sincerity and heart." according to the Straits Times
This is finally admitting that we've known all along, that North Korea isn't developed. Does anyone have any theories as to why he would tell this to an adversary out of everyone?
Like you said, everyone already knows. If Kim is really seeking better terms with the world, continuing to spout obvious falsehoods won't help him much. This way he appears more sincere.