You are indeed correct. I recalled that the nginx migration was in progress until around the time of 5.4, but did not remember that it was in base at the time. Thank you for correcting me, it was indeed in tree from 2011 to 2014.
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...