Why it works:
The tough tunica surrounding your smooth muscles consist basically of 2 layers. One is for longitudinal expansion and one is for circular expansion. If you want to gain girth you must increase the size of the circular tunica. You can either do this by increasing the pressure through well known exercises such as jelqs, ulis, clamping etc. or by twisting your penis and pulling it. Since this exercise is so intense and can be very painful if you push yourself too far it is not far-stretched that they are more powerful than regular girth exercises.
I have troubles understanding how twisting your penis and stretching it should expand circular tunica. Not saying the exercise doesn’t work, just that the explanation of the ‘why’ doesn’t make much sense to me.