If you listen to Conway talk about the Surreals you'll note that he considered it a game (in the game theory sense). He was interested in games of a certain kin

If you listen to Conway talk about the Surreals you'll note that he considered it a game (in the game theory sense). He was interested in games of a certain kind and what properties they had, a long the way he stumbled upon this game that we now call the surreal numbers.