The authors don't state at the beginning what version of OpenBSD they tested, but the refs at the end refer to 3.8, which is more than a year old (4.0 is out, with 4.1 in the wings).
They also state that there is no firewall graphing software for OpenBSD, but pfstat has been in OpenBSD's ports tree since 2002/07/26. pfstat bills itself as "a small utility that collects packet filter statistics and produces graphs." To try it out just do<br/>
cd /usr/ports/net/pfstat; make install <br/>with the appropriate privileges (e.g sudo).