That still doesn't involve pulling records from random servers like registrar's DNS server for domains they are not yet authorative for.

No, it doesn't, because nobody is configuring systems to query that registrar's DNS server for zones it doesn't own.

What you are describing is a forwarding DNS query resolver, which can be configured to directly answer queries without forwarding them upstream in the DNS hierarchy. This is sometimes used for ad-blocking, but the archetypical example is the DNS resolvers your ISP usually provides. Their purpose is to forward your queries to the nameserver responsible for the zone you ask about.

Domain registrars, however, usually do not operate forwarding DNS resolvers. They typically only answer queries for zones that they are responsible for, and give you an NXDOMAIN response for anything else. For this reason, nobody would use a non-forwarding DNS as a resolver for their computer since it would make it near impossible to reach hosts on the Internet (unless you happen to query a record for one of the zones they provide service for).