This... kinda depends on your perspective? There are many ways to look at it.
Are "game files" all files related to the game, including saves? Basically, if it's used by the game, it's a file used by the game. Resource, input, temporary, whatever, it's a game file.
Or are they just the files that make up the game proper, with music and saves being an external input? Depending on game design, it is entirely possible that components such as save data are completely external to the "game". At this stage, do you consider these external components to still be "game files"? Some might, some might not.
Even when they are internal, though, there can exist a perspective that "game files" only refer to things that run the game engine itself, and not the resources that are used. So one might consider all the actual graphics objects and such to not be "game files" if they're resources that are read by the code, even if they're still much internally stored within it.
It gets complicated based on the system. Take an emulation system that allows you to make save states. They're kinda independent files of data that you can manipulate all you like if you're knowledgeable enough, without necessarily manipulating the game's actual data. You're manipulating only a state. Would these be classified as game files?
More relevantly, I guess the question becomes to what importance this distinction is. People have differing opinions on terminology and I don't think this site really needs some hard-defined standard for it as long as people make themselves clear in their posts or in clarifying comments.