But it's not a misconfiguration, it's a bug as the article explains. And it's not the author's fault that Apple named their firewall the same as OpenBSD.
It's not a case of naming something similarily to other software. OSX used FreeBSD's ipfw and around the time they renamed the OS to macOS, they switched to OpenBSD's pf.
Now they've screwed up either configuration or implementation but to me - it doesn't read like a bug in pf.
I believe Apple used FreeBSD's implementation of pf, as it also has the same syntax. OpenBSD pf has evolved since then and their are minor syntactic differences for some rules between freebsd pf and openbsd pf.
