Here's what one of the pros who played against AlphaStar had to say about it:

"MaNa: I would say that clearly the best aspect of its game is the unit control. In all of the games when we had a similar unit count, AlphaStar came victorious. The worst aspect from the few games that we were able to play was its stubbornness to tech up. It was so convinced to win with basic units that it barely made anything else and eventually in the exhibition match that did not work out. There weren’t many crucial decision making moments so I would say its mechanics were the reason for victory."