I don't think the uncanny valley concept is really applicable here, unless the file manager resembles a human. It's certainly a departure from the expected behavior, though.
Anything that looks almost like what you expect, but is not quite what you expect, can qualify as falling into the uncanny valley. That term doesn't exclude definitions outside of robotics / AI but really applies to any UI.
A good example of this is trying to emulate OS UI (like a file manager that looks like Windows or MacOS) in a browser using Java - this used to happen more than it does now. But whenever you interacted with it, it wasn't quite web UI and it wasn't quite OS ui - even though it was trying to be.... It was really terrible UX and has since fallen out of favor and been replaced by UI that is clearly web - Dropbox's website is a great example. That's because it fell into the uncanny valley.
TLDR; if it almost does what you expect, but not quite, it could be uncanny valley.
A good example of this is trying to emulate OS UI (like a file manager that looks like Windows or MacOS) in a browser using Java - this used to happen more than it does now. But whenever you interacted with it, it wasn't quite web UI and it wasn't quite OS ui - even though it was trying to be.... It was really terrible UX and has since fallen out of favor and been replaced by UI that is clearly web - Dropbox's website is a great example. That's because it fell into the uncanny valley.
TLDR; if it almost does what you expect, but not quite, it could be uncanny valley.