I wonder if the sudden walk-out was planned by both leaders so they could go home and say, “See we are being tough on the other guys!” Then they could come back and agree to some of the things they did not agree to on this trip. And now that the South Korean leader has said he will involve himself again, he can continue to bridge the gap and keep the negotiating process moving forward.
No, I don’t think it was planned though it was clear before they met that if things did not go accordingly ‘walking away’ was certainly on the table. That’s how Trump works...because walking away is also a deal.