We're working on a new/updated guide to kegging that will replace this guide which is based of a 20+ year old article. In the meantime, we have updated the purging portion using information from Jeff Rankert (thanks Jeff!).
We (the AHA) really appreciate this type of feedback/attention, and if you ever come across similar instances of outdated/incorrect information please don't hesitate to shoot me an email! duncan@brewersassociation.org
-Duncan, AHA Web Editor