It is a neural network trained, in part, against the text in the game manual.
Of course, it's considerably more complex than that in the theory and implementation. :D
1. That's gotta be one helluva manual
2. Reversing the procedure to automate documentation by examining variable and method names along various code paths would be brilliant.
Teaching ultra-intelligent AI Monopoly, though? - guaranteed robot overlords.
It's not learning to play the whole game. It's learning to cheese (in gaming parlance) the opponent. The strategy it learns is to build a warrior as fast as possible and go and attack the enemy's city. If that fails, it almost always loses. The manual gave it some hint in that direction.