Why is a user created when creating a share

I've also noticed the link from the root to the share is owned by the named owner, but the actually directory is owned by nobody (except media - what's up with that?)! The link is what is exported (for NFS) and bind-mounted (for FTP).

Link from root of file system:

lrwxrwxrwx    1 backup   users           9 Jul  8  2008 backup -> /c/backup
lrwxrwxrwx    1 document users          12 Sep  7  2008 documents -> /c/documents
lrwxrwxrwx    1 media    users           8 Jul  8  2008 media -> /c/media

Actual directory in /c volume:

drwxrwsr-x   12 nobody   users       16384 Feb 26 21:30 backup
drwxrwsr-x    8 nobody   users       16384 Oct  5  2013 documents
drwxrwsr-x    8 media    users       16384 Aug 22  2014 media

NFS exports

"/backup" 123.123.123.0/255.255.255.0(insecure,insecure_locks,rw,async)
"/documents" 123.123.123.0/255.255.255.0(insecure,insecure_locks,rw,async)
"/media" *(insecure,insecure_locks,ro,async) 123.123.123.0/255.255.255.0(insecure,insecure_locks,rw,async)

FTP mounts

/backup            /home/ftp/backup     bind       bind              0      0
/documents         /home/ftp/documents  bind       bind              0      0
/media             /home/ftp/media      bind       bind              0      0

I wonder if that is relevant, or if the link could just as easily be owned by nobody or root?