The DNS software administrator has not removed the root hints file on an authoritative name server in order for it to resolve only those records for which it is authoritative, and ensure that all other queries are refused.

A potential vulnerability of DNS is that an attacker can poison a name servers cache by sending queries that will cause the server to obtain host-to-IP address mappings from bogus name servers that respond with incorrect information. The DNS architecture needs to maintain one name server whose zone records are correct and the cache is not poisoned, in this effort the authoritative name server may not forward queries, one of the ways to prevent this, the root hints file is to be deleted.
When authoritative servers are sent queries for zones that they are not authoritative for, and they are configured as a non-caching server (as recommended), they can either be configured to return a referral to the root servers or they can be configured to refuse to answer the query. The requirement is to configure authoritative servers to refuse to answer queries for any zones for which they are not authoritative. This is more efficient for the server, and allows it to spend more of its resources doing what its intended purpose is; answering authoritatively for its zone.