It is an open source project with both commits and discussion happening in the open (tech@ in particular), so the barrier to understanding is reasonably acceptable. At some point it was also debated to move to nginx, but in the end httpd(8) was championed as a natural offshoot from relayd(8) which was already in base.
https://www.openbsdhandbook.com/services/webserver/nginx/#:~....
OpenBSD httpd would probably have never existed if nginx upstream reacted differently.
https://www.openbsd.org/papers/httpd-slides-asiabsdcon2015.p...
[0] The OpenBSD nginx port still includes the default chroot patch, ~8 years later, see https://raw.githubusercontent.com/sthen/nginx_chroot_patch/a... and https://github.com/openbsd/ports/blob/master/www/nginx/Makef...