Shall we play a game?
The one interesting thing about this is that they helped it learn how to trim down the decision tree to a manageable size by having it play games against itself. Reminded me of War Games, playing tic tac toe with number of players '0' lol.
But I agree 100% with the other comments that beating a human at Go is not AI. It is still using search trees to figure out the best moves, just like it does in chess. Just like chess programs don't bother examining every possible move because they know to trim the decision trees of irrelevant stuff, so does this Go program. It just requires much more trimming since the decision tree is so much larger.
We'll have real AI when you have a program that knows absolutely nothing about Go, but is able to learn to play from reading the rules, reading books about 'how to play', reviewing past games, playing games, etc. and THEN beats the world's best. Being able to follow an algorithm someone else wrote that tells it the rules / goal of Go, provides it the logic about how to trim the decision tree and so forth is not "intelligence". It just a really really really fast and accurate trained monkey.
You'll have the kind of creative intelligence people do when it can take that world class playing ability and suggest variations or handicaps it thinks might be more fun to compensate for its opponent's relative lack of skill (hopefully with the emotional intelligence not to unduly insult the world's best human player when doing so :)) Or maybe "let's invent our own game using the Go board and the pieces from a Monopoly set and make up the rules as we go" as typical grade schoolers might do if you left a couple of them alone on a rainy day when the power's out and all they had to play with was board games.