Why not a subdomain under one of the public domains he already has?

For interactive use you'd typically only use part of the domain anyway, with correctly set up search list. Also has the advantage of easily making some hosts available via IPv6 to the outside - or with split horizon DNS and a gateway host expose specific services, where inside connection directly goes to the specific host, and outside via a reverse proxy.

Overall he's just describing a typical simple internal DNS setup - from the title was expecting him to talk about how he got a stable authoritative DNS server for his public domain running at home (and how he got around the "two nameservers" requirement).

On the plus side, that made me realize that my current home connection _is_ stable enough to host one of my three authoritative DNS servers, which should save me about 7 EUR per month.