Digit DP counts over a constraint space defined by digits. Next, we'll count over a constraint space defined by game states. Game Theory DP models two-player games. Instead of "how many numbers", you'll answer "who wins with optimal play". The key idea is similar: define states, compute transitions, propagate answers.
But the transition is adversarial: your opponent picks the worst option for you. Make sure you understand digit DP's state design. Game theory DP adds complexity with min-max alternation.