The bots in this particular game had the ability to learn effective strategies where the aim is to kill the other players and not be killed. He put sixteen of them in a match together to see how good at the game they would get, and if they would become essentially invincible against a mere human...
And he completely forgot about them. He remembered four years later, and went to check on them.
After learning, adapting, and evolving for four years, he came back to his bots and assumed something was wrong.