This is, of course, water well under the bridge by now. However, I think that Brian's understanding of the rule amendment would have made the amendment superfluous. The text of the original rule (before it was amended) would have always required a 2/3 vote on the main motion, no?
In any event, if the PB was in error, its unfortunate, but only because the rules should have been whatever the body agreed. This possible misinterpretation of the rules did not have any practical effect.