If AlphaStar is playing at the top of the ladder it probably won't be too hard to figure out that it's AlphaStar. There's only around 15 or so players with MMR above 6000, and they tend to know who they've been matched up against, even if the opponent hides their name with a barcode (they name themselves "IIIIIIIIIIII" so you can't recognize who it is. And AlphaStar has a pretty distinct play style too.

Unless it's playing more towards the middle of the ladder where there's lots of players I don't think the test would be very anonymous. Regardless, I'm pretty excited to see what happens. Hoping to luck into a game.