IkiWiki::backlinks returns a form of $backlinks{$page} that has undergone a lossy transformation (to get it in the form that page templates want), making it more difficult to use in other contexts (like pagestats).
A commit on my among branch splits it into IkiWiki::backlink_pages
(which returns the keys of $backlinks{$page}, and might be suitable for
exporting) and IkiWiki::backlinks (which calls backlink_pages, then performs
the same lossy transformation as before on the result).