The version of OpenBSD's pf that was ported to FreeBSD/NetBSD is ancient, 4.0/4.2 era and lacks recent development.
It may indeed be better than whatever else is available for FreeBSD/NetBSD, but there have been some fundamental changes in configuration syntax with the recent releases of OpenBSD, especially around scrub/nat/rdr rules.
So if you're going to use OpenBSD's pf documentation, you may wish to grab an older PDF copy from
here.
Peter N. M. Hansteen's
Book of PF would still be helpful for FreeBSD/NetBSD users, and for smaller configurations his famous
pf tutorial is still updated occasionally.
The FreeBSD/NetBSD folks need to stop referring to OpenBSD for their outdated fork of pf, as do users of those operating systems.. as it's only going to frustrate them.
Good luck.