Many people, including myself, tend to look at .arpa and think "oh yes, thats PTR queries" but forget the DNS doesn't have a global rule that ONLY the PTR query can be sent to the domain.

It's just a domain. You can put anything into your zone. A, AAAA, PTR, TXT, you can even put HESIOD records if you want to party like its Kerberos nineteen ninety IV.