Yep, MC has imported the files both via a drive letter or URI, and via the DLNA server on the NAS. Port 2869 is one of the two UDP ports used by UPnP to advertise a UPnP/DLNA server Port 1900 is the other. . Each time you reconnected to the NAS by opening our Jukebox library, MC re-established both versions of the file, one via each path, therefore creating duplicates. It wouldn't matter that Auto Import was turned off, as MC already knew about the files.
As you have deleted the DLNA versions from your Library they shouldn't reappear. I really hope you didn't also delete them from the disk, but then I don't think a "delete from disk" request would work to a DLNA server. That may be DLNA server setting controlled, so you may be lucky that you didn't just delete all your media files from your NAS.
What to do now?
Turn off the DLNA Server on your NAS. If you don't need it for other reasons, there is no reason to leave it running for MC.
Make sure that Auto Import settings do not include the DLNA Server anywhere.
Turn Auto Import back on in MC and enjoy the music.