Where does the dust particles comes from?
From the video, the author's the lens was never changed and so the dust cannot come from external source.
If it is already in the camera during production, this problem should go away after a few cleaning but many owners still report the problem.
One possibility is the particles are release by the fraction caused by the moving parts like the mirror assembly.
When I own D700 some years back, I only need to clean the sensor once in a while due to dusts.
I'm using m43 system now and I never once need to clean the sensor for dust problem even after using the camera after a few years.
The flipping of mirror could be one cause for the dust but if the dust keep appearing even without changing the lens, something is really not right and it is appearing only on the left side of the sensor.