Talks between world leaders are usually not open to the public. That is entirely normal and necessary.
I agree. That is why I found it so worrying that Trump could not talk to the media without blurting out a reference to it. These kinds of back channel discussions are often derailed when they are disclosed prematurely. In fact, I did not even like it when Rex Tillerson suggested there were attempts to negotiate (albeit with Trump telling him to abandon those attempts). I desperately want the North Korea issues to be resolved without military conflict, and a negotiated settlement that freezes North Korea's nuclear arsenal in return for sanctions relief and formal Chinese guarantees of North Korean security is the best alternative. That involves politically uncomfortable compromises on all sides. The media, alerted that such discussions are underway, are going to be trying hard to find out the details.