Back to where / why / what this example is about.
The example , the image, shows quite a few signs of being a student example from a workbook and not a real world model for a machine. - right ?
The information in the image is way to thin/ non-existing to model this correctly.
"Twisted surface" can mean absolutely anything.
The "There is hint/note given in image to create twisted surface by line angle/normal to curve..."
can then , in a "student example for a different cad system" be a requisite for that other cad system to be able to fulfill the task.
It does not say anything about the shape at all!
If we divide the outer cylindrical shape as Bwsh has done, it is both "twisted" and "cylindrical". It fills the requirement "twisted".
The shape that Mmauldin created, is "twisted" but not cylindrical, - what more can we say about this particular shape ? - "un -defined" ?
"Linear sections" ?
There is an unlimited number of shapes a curve can have between two points, and "twisted" does not help much. Neither does the supplied image.
Regards,
Tomas