More than 3 countries for 72 hour twov

I am a US Citizen traveling from New York, then traveling through Thailand, Cambodia, Vietnam, Shanghai (only), direct back to New York. My dates in Shanghai are 05 NOV, arriving at 14:00 and departing 08 NOV at 11:00 AM. Does this qualify for a 72-hour free transit; or because I am coming from Vietnam (not a qualifying country), am I not allowed to us the free transit option?