AlphaGo doesn't know anything about the game of go. It "just" manipulates symbols, runs instructions on its CPUs and GPUs, illuminates pixels on the screen for a human to see.
It just also "happens" to be the case that if you interpret those pixels as go moves and play those moves against the world champion human go player then eventually that human will hold a press conference announcing to the world that AlphaGo has won the match.