Interesting. It may be possible that while the style of play of Master is able to exploit the errors of human players easily and score convincing victories by many stones, Zero is closer to playing Go perfectly, even if it means winning by one stone. There is a chance that Zero would not score such convincing victories over humans as Master but is much less exploitable. If a strong player plays obvious novices (and humans are now at a level of novices compared to these programs), it doesn't have to worry about taking more unsound risks.