The story below the video said she was trying to commit suicide and jumped in the water and some boatmen rescued her.
Or maybe it's way to have water exit the lungs via gravity.

I'm not a doctor but I have training in the Heimlich maneuver and CPR. This upside down thing is kind of interesting, how and why it works.
I can see how it is more feasible in China with smaller people, but in America where there are more obese people, laying a person down and pressing on their chest is better. Ain't no way I'm flipping a 300 lbs. dude or woman upside and carry him or her over my shoulder.