DeepMind was able to bootstrap their program with human data, but then gradually remove the biases present in human play. It’s impossible to know how well they have succeeded in that, but surpassing human level to the extent they have done is already a huge step.
Lessons from Alphago: Storytelling, bias and program management
Carl Johan Ragnarsson

This isn’t entirely accurate, although it describes the AlphaGo we saw last year. What played Ke was different.

Please see:

"... about a year ago, DeepMind redesigned the system. In essence, they built the new AlphaGo without help from human moves. They trained it entirely from games where the machine plays against itself--part of a continuing progression toward AI techniques that truly learn on their own. 'AlphaGo has become its own teacher,' says David Silver, the project’s lead researcher."