This is actually more impressive about AI. People used to think Go AI wouldn't be able to beat a human player until like 2050. I certainly thought that when I learned it in like 2010. Back then the strongest AI was like 1 Dan (amateur) at most. (9 Dan is the highest rank and professional 9 Dan which you need to play professional games to get to are much stronger than an amateur 9 Dan which is like 9 Dan from an online website. Also the games rankings go from 30 kyu which is the lowest rank to 1 kyu which is the highest "amateur ranking". After 1 kyu is the Dan ranks ranging from 1 to 9)