Without decompilation, it's impossible to say that you've experienced every aspect of a game. So AI will be able to build something that approximates part of the game from video of gameplay, but it will not be able to completely build the game with reliable consistency.
Every possible thing! We can't even enumerate every possible thing in chess with a compact set of rules let alone every possible thing in something like Red Dead Redemption with unbounded complexity. "Thing" is not "what happens when you shoot an enemy". "Thing" is "what happens when you shoot this particular enemy in this particular place at this particular in-game time and this particular not-in-game time after doing this particular long sequence of other very particular things".
That's what the issue tracker is for. If someone notices a subtle difference and they want it added they'll file an issue. If nobody notices the untested space it doesn't matter.
In general I agree, but in the context of this specific thread what you're saying is a mathematical impossibility. Now could you use pure observation to get the gist of a game and maybe even have AI fill in the rest with fun new details? Yes. And what you'd end up with is an approximation of the game missing some things and adding others, not a clone of it. But you can't use pure observation to form a complete solution of a game when there are more possible game states to enumerate than there are Planck times left until the heat death of the universe.
