That is when there is an explicit PTR record, for instance one of my assigned addresses can be named that way due to:

    74.231.187.81.in-addr.arpa. 3600 IN PTR ns2.nogoodnamesareleft.com.

in the zone file for that IPv4, but unless they've explicitly configured, or are using a hosting service that does it without asking, this it won't be what is happening.

It isn't practical to do a reverse lookup from “normal” name-to-address records like

    ns2.nogoodnamesareleft.com. IN A 81.187.231.74

(it is possible to build a partial reverse mapping by collecting a huge number of DNS query results, but not really practical unless you are someone like Google or Cloudflare running a popular resolution service)

Not sure what you are trying to tell me. This isn't guaranteed to work. If you define a reverse lookup record for your domain, then that counts as published in my book.

I love how the ARPANET still lives on through reverse DNS PTRs.

https://www.youtube.com/watch?v=V78GUSOS-EM