"On his clients" meaning his eg laptop. Personally my laptop uses its own preconfigured DNS servers, even (especially!) at coffee shops/etc because the coffee shop's DNS isn't to be trusted but more than that, they are frequently extremely slow. (It does take some fussing if there's a captive portal, but that's easy enough to handle.)
That is fair, I suppose, but why use a different DNS server than the default for your home network? I still think there's something fundamentally wrong with a DNS configuration that breaks Windows connectivity tests.
I do hope you're using something encrypted. Plain DNS can be redirected and manipulated quite trivially.