The “other” (or “world”) are those users that neither own the file or directory nor are members of its group. Unfortunately, /mnt2/root does not have anything to do with the root user (unlike /root), but is a btrfs subvolume representing the root of the filesystem. This issue has been touched upon in the following post and related github issue:
The result is that a lot of the files on your filesystem now not only have the wrong permissions but are also owned by the wrong user/group. This is technically repairable through SSH if you have a reference system (e.g. a VM) with correct permissions. However, it will be a lot of work and you’re probably better off reinstalling.