In the video for the second match, a Google employee mentions that a neural net they call the policy net (trained on a large sample of historical games) provides intuitive moves, while another NN evaluates board strength. They apply the policy net to find multiple interesting moves, then continue to apply the net to anticipate the opponents moves to generate a tree of possible moves. It then just settles on which move to make that gives it the best odds of winning

Starts at 42:00 https://www.youtube.com/watch?v=l-GsfyVCBu0