Is this using a relay to check kind 0 and whoever was the first to use a nip05 with that domain is who it returns?
If you have your own domain, you can tell people to find you on nostr with it
Example: "find me on nostr as utxo.one"
And you can link it like https://njump.me/utxo.one
Discussion
It only works if you use the "_" key in the nostr.json file, clients probably all do this search in different ways tho