He's the generally agreed world's best player (and only 20-years-old). but he might not have seen the true strength of AlphaGo. After analyzing the games, it's apparent that AlphaGo only tries to win, and does not try to win by a large margin. Translate that strategy into game play, AlphaGo seems to always try to stay ahead of its opponent by a few points, and often trades an optimal move by a less-profitable one but one that's much safer. So even though the two games with Lee have been close, no one has any idea how strong AlphaGo really is.