That's instantaneous APM, not general APM over the course of the game. The human player's instantaneous APM went well past 1000 at certain moments during the course of the matches, too. All that means is a few clicks as fast as possible.
So when AlphaStar is doing 1000-1500 APM, there's no way a human could do that or compete with that. This doesn't impress me because it's obvious if you create something that can do something way faster than a human it will win.