It's not from systemd though. glibc's NSS stuff has been around since... 1996?, and it had support for lookups over NIS in the same year, so getaddrinfo() (or rather gethostbyname(), since this predates getaddrinfo()!) have never just been DNS.

systemd-resolved normally does use a separate protocol, specifically an NSS plugin (see /etc/nsswitch.conf). The DNS server part is mostly only there as a fallback/compatibility hack for software that tries to implement its own name resolution by reading /etc/hosts and /etc/resolv.conf and doing DNS queries.

I suppose "the DNS compatibility hack should follow DNS RFCs" is a reasonable argument... but applications normally go via the NSS plugin anyway, not via that fallback, so it probably wouldn't have helped you much.