It’s not really a big deal, but it’s “nice”, philosophically speaking: all the tools the author uses are actually included in the base OpenBSD system whereas on FreeBSD you have to install some packages.

OpenBSD places high value on providing an operating system that is so-called “secure by default” meaning when you install it, you shouldn’t need to perform any hardening in order to achieve maximum security so long as you are careful in your configurations. They also try very hard to provide a diverse range of high quality tools to minimize the need to install external packages as these packages cannot be practically subjected to the same level of scrutiny as the base system.