IMHO the XBMC wiki isn't so good when it comes to music video. It's also a problem of how skins deal them. From what I've seen in default Confluence, Music video behaves like other video db items, but there is also linkage in the skin to "artist" and "album".
I believe XBMC will parse the filename in the video library update process expecting something like artist - songtitle. Those are used by the scraper to compose a search url to scrape data on the file (unless you have a paired nfo file). The video database will update musicvideo data table with title, artist, and album (main metadata). A link to art will allow a thumb, poster and fanart assigned to each MV file. Also, the artist is stored into the actors table and an artist (actor) thumb can be saved. I know thumb can be generated from the MV file itself (if auto-thumb is selected in settings options). I don't know exactly how local art is selected (for example, folder.jpg, fanart.jpg from containing folder).
It seems like MV artist and album data can also be used to find details in the music database, but I'm not sure how that works or maybe I am wrong on this. Note that MV doesn't have a concept of "album artist".
Personally I have my musicvideo source set up musicvideo\artitstname\albumname\. I haven't figured out how best to store local art.
Anyone else can correct or provide more info would appreciate it.