It is fundamentally unimportant how the gains occurred unless the player had an inside role in the software development. Nobody is doubting that it is statistically improbable that a player won this amount. The player is not responsible for knowing if a game is flawed or not. It is also unimportant whether other players won or lost on this game. Your experience "over the years" with other games you've seen is not a credible comparison either.
So that leaves the book with two options... suspend all future payments and provide evidence of the exploitative play and demonstrate that he knowingly used a flaw in the game to win... or just pay him.
So that leaves the book with two options... suspend all future payments and provide evidence of the exploitative play and demonstrate that he knowingly used a flaw in the game to win... or just pay him.