It depends on what is meant by machine learning. If it's referring to learning games from first principles, then it's certainly true for the time. As far as I know the first AI to be able to learn multiple games from first principles was demonstrated in 2015:

http://www.wired.co.uk/news/archive/2015-02/25/google-deepmi...

AlphaGo wouldn't fit in this mould, as it has been taught how to win at Go rather than working it out from the basic rules, so AI hasn't 'beaten' Go fully, but AlphaGo is a great achievement nonetheless.