The point of the exercise is to see if the candidate can code their way out of a damp paper bag. This is the kind of pedantic bullshit that's all about showing how clever you are at the expense of understanding what's going on.

If you're clever enough to know that "copy a file" is an incomplete description of what a user actually wants or needs, you should be clever enough to know that "point out as many edge cases to confound a simple interview coding question as you can think of" is not what the interviewer actually wants or needs with that particular question.