I had to Google on "steb" drive to see what it was. In the metal turning world there's a somewhat similar device known as a "drive" center.
The drive center is a little more complicated mechanism allowing a blank with a rough, irregular, unprepared end to be held between centers and power rotated with no slippage in heavy cutting. Once in awhile you'll see production parts with the telltale marks left by the drive center, usually where cosmetics of the part are not important. The manufacturer saves maybe a 1/4 to 3/8" of material that would be wasted by trimming off the marked end plus the time to fixture the part for a trimming operation.
My guess is the handle shown was made on a high production machine and somebody in the food chain made the decision that leaving the center markings on the end out weighted the added expense of end rimming.