No unknown users have been detected.
This means that all the users synced in the ownCloud's DB (for LDAP in this case) exists in the LDAP server. Unless a user is deleted in the LDAP server, the message should be the same.
Unless you modified the LDAP server, I don't see anything wrong. The log output might be nicer, but the output of the command wasn't intended to be dumped into a file, so I'm not sure if it's possible to improve it right now.