Perhaps I'm misunderstanding something, but this makes 0 sense to me. The Save button itself must be able to save the current state. So at the very, very least you should be able to just check on a schedule what the current state is and determine if it differs from the previously saved state.
There are much better ways to implement this that take more underlying work, but agree with the other comments, this has nothing to do with people not understanding files, it has to do with people expecting web editors to autosave.