Well the story was considered "completed" for a long time. Now that the author started a side story, it SHOULD be changed to "on going". It's just that it wasn't edited yet.
Ya a lot of stories were completed but have extra side stories but are never changed back to ongoing with the new side chapters. Like this one, obviously there’s supposed to be more chapters to this nee part but idk when or if it’ll be updated. Hopefully though
Wait it says “To be continued” so why does the status say “Completed” ╥﹏╥