Authoritative vs recursive DNS
A recursive resolver (like the one your ISP or 8.8.8.8 runs) does the legwork of a lookup for you: it asks the root, then the TLD, then your nameservers, and returns a final answer, caching it along the way.
An authoritative nameserver holds the actual records for a zone and answers only for that zone. It does not do the legwork for other domains.
This tool queries authoritative servers directly, walking the delegation itself, so it can show exactly which server gave which answer - something a recursive resolver hides behind its cache.