I'm not entirely sure whether this is a bug, but it has important implications either way.
Moderator only tags (like status-completed, status-declined, and featured) can only be added by, well, moderators.
However, in the case of featured, the tag is not permanent. A featured tag on a per-site meta or Meta.SE broadcasts the post in the site's community bulletin (or site-wide if coming from Meta.SE), and is removed automatically once the tag is removed by another moderator/employee.
However, as seen here, any user with full editing privileges on the main site or here on Meta.SE can use a rollback to make a post featured again.