I think it would be most useful to look at three different versions of Shimabuku Sensei showing the dump from Wansu kata. That will allow us three slightly different angles of his performance.
Now the Isshinryu standard (based on decades of internet discussion) example of how this throw is done against an opponent is probably that of Arsenio Advincula from his YouTube site.
Sherman Harill from a clinic focusing on Wansu kata in 1998 in Derry New Hampshire. From my personal notes .
Attacker Right foot forward Left Punch
1. First you draw back in a left cat stance, your left open hand held above your head and your right open hand drawn back to your right hip with the fingers pointing down.
2. As they step in with the strike you slide into the attack with your left hand rising under their arm to lift it up. At the same time you slide forward shifting to the left into a horse stance while your right hand strikes toward their groin, This stops their forward momentum.
3. Your left hand slides down their arm to hook over their wrist. At the same time your right hand slides up placing itself on their arm behind their elbow. The two motions act as a vice on their arm. The left pulling down, the right rising up.
4. The previous technique causes them to shift forward on their toes. When you struck their groin it caused them to rise on their toes, then the following motion destabilized them to begin to fall forward.
5. As they are falling forward, you do the 180 degree turn, at the same time the pressure against your wrist you are pressing it into your left waist chamber. As that is happening the right presses against their elbow making them fall forward as you move forward.
There were several variations of this principle shown.
Mark Radunz’e version of the Wansu dump application is interesting. He was a Sherman Harrill student.
In his application you do not even use the body turn.
Finally a non-Isshinryu alternative for the Wansu Dump.
These are just a few of the possibilities that the movement offers.
With work you can develop new options too.
As an Isshinryu practitioner who has also studied Judo, This is how I interpreted the throw