I am thinking that you have ReadyDLNA enabled on the NAS, and that you are accessing the files via a DLNA client (for instance, a smart TV). Is the case?
If so, the files do (or did) exist somewhere on your NAS, but they would not be all in the same folder. ReadyDLNA is simply showing all the videos that it found in all the folders. If you don't actually use DLNA, then you should turn ReadyDLNA off, and this folder will disappear entirely. It is also possible to do a manual scan for media, and that would refresh the database that ReadyDLNA uses.
...and you are absolutely correct, I do use a couple of DLNA clients to play the media from my NAS - one a smart TV as you had suggested, and one set up on an Android tablet to play music.
Hence, the option to perform a manual scan for media sounds like what I need to do. You are also correct that the entries in the "All Videos" folder are just 1 second clips of things I must have watched online and completely forgotten about. I guess they are not taking up too much space, but they appear on my TV screen when I am choosing what to watch, so I'd prefer to get rid of them.
Thank you so much for your most helpful comments. I will look up how to do as you suggest. I'm so glad I came to the forum with this question, as it had been impossible to find an answer online.
