The celebrity puts a TXT record in their domain name which is in their profile - the imposter also puts the same domain in their profile (they always do )

The domain tells the client what the true npub is for that domain - when I wrote the original article we released a proof-of-concept chrome plug-in that shows the concept in action 

https://easydns.com/blog/2022/08/05/solving-the-fake-twitter-profile-problem-with-dns/