Cathay Pacific's information on excess baggage from the Americas is somewhat unclear. I'm hoping someone out there has some experience and can clarify for me?

Per this page, if I am flying economy from the US to Bangkok my allotment is two bags, each one max 50 pounds.So far, so good.

Here's where it gets confusing. When I look at their extra baggage information here, it indicates that if I check a third piece of luggage it will cost me $150. However, what is not clear is whether that $150 gets me an additional 50 pounds in my baggage allotment or if paying $150 gets me an additional bag, but all three bags still have to come in at 100 pounds or less. Yes, "Charge for baggage in excess of the free baggage allowance is calculated by piece at the applicable extra baggage charge on a zone basis listed as below," but that seems a bit unclear.

Any insight? I'm actually moving, so the weight issue is a huge item for me!