I did that. Mapped drives and the NAS show typical windows paths inside of explorer. It's only inside MC19 that I see the network paths described earlier.
Did you map the drives before importing the media into MC?
You could try reimporting one or two files to see if they import with the correct path.
There are solutions to fix your problem, but it might be easier to just reimport the media.
The fix involves the Rename Move Copy feature and using the Find and Replace section in "update only mode". Basically, without moving any of the files physically, you tell MC to change the path it looks for the files.
However, the path you are showing is a bit strange: Are you sure you're not using your Nas's DLNA server functionality instead of MC's library with imported media?