When you select the top-level Playlists item in the Tree, it shows the "contents" of ALL Playlists in the File Listing. So, the reason those files are showing up there is that they ARE included in (at least one) Playlist: The Recently Imported one Jim mentioned, if not others.
But the key to understand, is if you select a View in the Tree, it always shows the results of itself, and those "under" it.
I have no playlists, and nothing in playlists; so why it is showing all my albums in top PLAYLIST view? It is different in Windows MC, there is nothing showing there.
I had no explanation so far why MC's in two different OSes behave in different way.
I think it is a bug in Mac version.
I suspect that I will have all my albums displayed there. As for now I am testing everything before importing thousands of albums into MC.
it is easier just with 4 albums. I can do all kind of experiments. Importing, deleting etc., to reach the best setup for MC.
cheers,