I started using Bookmark+. Haven't customized it at all, it seems its using the left half of the screen to show what seems like "duplicate" information.
As I using this tool right?
M-t) shows the file names of the bookmark targets (or the buffer name, if the targeted buffer has no associated file).
In your case it looks like you named the bookmarks the same as the files. You might have done this yourself, explicitly. Or you might have done it implicitly, by creating autofile bookmarks.
The name of an autofile bookmark is the nondirectory part of the file name. In the case of your screenshot, it seems that all of the files (second column) are in the same directory, which is the directory listed at the top of the display: