Nikon users consider NX edits of the raw file "non-destructive" because it can be reverted to the original image. No data is lost and none of the rawe data is changed; just some text tags are changed. You may consider "non-destructive" to have a different meaning, but I would argue that since nothing was destroyed or irrevocably lost, it is "non-destructive"
This is all just semantics of course, but the term has this specific meaning to a Nikon user.
To add to this, Nikon Capture edits are as non-destructive as are the changes you make to the IPTC/XMP and then save them to the RAW file (e.g., as PM allows). In this case also only the IPTC/XMP tags are overwritten, without altering the RAW image data itself (the file itself is changed, however). With Nikon Capture, the
edit steps are written to a special exif tag, leaving the rest basically untouched (the embedded jpg is also updated).
Note that this ability to store the edit steps within the RAW file, without altering the underlying raw data was actually one of the key reasons for me to start using Capture instead of e.g., Photoshop to do my raw editing.
Cheers