Great.....WHAT IS YOUR POINT?
I think the point is that the IFBB Rule Book applies to both amateur and professional bodybuilding. The webpage states "Rules and Regulations governing the sport disciplines of Men's and Women's Bodybuilding, Men's and Women's Fitness, Women's Body Fitness and Men's Classic Bodybuilding". Since there is no pro classic bodybuilding, the rule book is meant to cover the amateur branch of the IFBB.
The IFBB claims to be a federation. A federation is "an organization or group within which smaller divisions have some degree of internal autonomy". The smaller divisions are the country organization. In the US, that is the NPC.
The NPC is the US branch of the IFBB, just as much as the CBBF is Canada's and UKBBF is Britain's. So if the IFBB's rule book applies to athletes, judges and officials in the IFBB affiliate in Bahrain, it applies to the people in the NPC.