Judging by some YouTube videos I’ve seen, ChatGPT with GPT-4 can get pretty far through a game of chess. (Certainly much farther than GPT-3.5.) For that duration it makes reasonably strategic moves, though eventually it seems to inevitably lose track of the board state and start making illegal moves. I don’t know if that counts as being able to “actually play a game”, but it does have some ability, and that may have already influenced its answers about the other topics you mentioned.
What if you encoded the whole game state into a one-shot completion that fits into the context window every turn? It would likely not make those illegal moves. I suspect it's an artifact of the context window management that is designed to summarize lengthy chat conversations, rather than an actual limitation of GPT4's internal model of chess.
Having an internal model of chess and maintaining an internal model of the game state of a specific given game when it's unable to see the board are two very different things.
EDIT: On re-reading I think I misunderstood you. No, I don't think it's a bold assumption to think it has an internal model of it at all. It may not be a sophisticated model, but it's fairly clear that LLM training builds world models.
We know with reasonable certainty that an LLM fed on enough chess games will eventually develop an internal chess model. The only question is whether GPT4 got that far.
So can humans. And nothing stops probabilities in a probabilistic model from approaching or reaching 0 or 1 unless your architecture explicitly prevents that.
Or, given https://thegradient.pub/othello/, why wouldn't it have an internal model of chess? It probably saw more than enough example games and quite a few chess books during training.