PKG_PATH is set and pkg_add automatically adds details to make it point to a package.

With PKG_PATH set (he does it in the .profile in the blog post)

pkg_add pkgin becomes pkg_add https://cdn.NetBSD.org/pub/pkgsrc/packages/NetBSD/$(uname -m)/$(uname -r | cut -d_ -f1)/All/pkgin

I prefer to do it that way since pkgin has its own repository config, and if I use pkg_add after installing pkgin it'll be to install packages from the pkgsrc and that might clash if PKG_PATH is set.

I know it seems contrived.

https://www.netbsd.org/docs/pkgsrc/using.html