Definitions of "originating country" and "third country"

The rule is that the originating country/region and third country/region cannot be the same. But does "originating country" mean the country you were in before China, or your home country? For example, you can use the waiver for LAX-PVG-HKG, but not for LAX-PVG-SFO. I understand this. But does it work in reverse? I.e., can you use the waiver for HKG-PVG-LAX, if you are a US passport holder? In that case the originating country (actually region in this case) is Hong Kong, there is transit stopover in Shanghai, and the third country is the US. My Chinese friends are telling me they think "originating country" means your home country and "third country" means a country other than China and other than your home country. Can anyone confirm?