"Update cached metadata on device" -- means the metadata.calibre file on the Kindle which maps the on-device books to the in-library books.
Doing that will only update calibre's device view (not the books on your Kindle, in case you thought it would).
It is possible calibre doesn't update the device view icon to indicate that the cached metadata has been sent (well, that file is also refreshed from scratch whenever you send a book as well). But it has, anyway.
If you disconnect and reconnect your Kindle it should show the updated metadata in device view.