It has always been there, with the exception that it was only available for one single IP address in the past whereas it now extends to all addresses. This not to justify it. However, it is not a hard-coded as in "you cannot change it" option. It is a run time option and you can easily change it to deliver the hostname for all the interfaces (next version) or easily disable it.
The option to change it to the hostname seems to make a lot of sense to me. Otherwise, when there is no accompanying record in /etc/hosts, an IP address of the host may not have a hostname at all. As I said, advanced users are able to switch off all the Pi-hole featured intended to be convenience features.