There seems to be some confusion about how this worked clouding the categorization of what to call it.
Let's compare the interfaces between how Shugart designated signals at the drive (and how other makers used them) vs how IBM re-designated them at the controller in order to support the twist idea. (I've used A and B on the IBM version to reduce confusion)
pin Shugart IBM before flip IBM after flip "2nd drive" interprets
10 /DS1 /MOTOR_A /MOTOR_B ignored
12 /DS2 /SELECT_B /SELECT_A /DS
14 /DS3 /SELECT_A /SELECT_B ignored
16 /MOTOR /MOTOR_B /MOTOR_A /MOTOR
IBM then jumpered all drives to use /DS2 on pin 12. And being standard Shugart drives (or equivalent) they expected their motor enable on pin 16 just as Shugart intended. So you have drives that, regardless of their actual role, expect one signal on pin 12 and one on pin 16, and don't pay any attention to what is going on at pins 10 or 14.
As such, the pre-twist drive connector becomes DOS drive B, presenting the original Shugart /DS2 select signal on pin 12, and the motor enable on pin 16, all in the very ordinary vanilla way (except that the BIOS should only set the bit to drive the traditional motor signal when using drive B)
But after the twist, the signal on the motor enable is what Shugart would call /DS1, but IBM is instead cleverly using as a "new" motor enable A. And the select signal arriving on pin 14, would be that which originated on the controller end pin Shugart would call /DS3, but which IBM is using as drive enable A.
Given that this scheme works with standard unmodified Shugart-interface drives, I'd categorize it as a clever "hack" or bit of manufacturing engineering. IBM changed only their controller card (which already had to be customized to match their bus design) and cable, and just bought the drives off the shelf.
You can see the manual for Shugart's longer-predating-the-IBM-PC original 1976 single-sided SA400 drive which originated this interface (as an evolution of the earlier 8-inch drive's interface) here. When Shugart extended the scheme to double sided drives such as the SA450 (still before the IBM-PC), they put four more places on the far end of the connector adding a side select and a "spare" and corresponding grounds, but didn't change the part of the interface used for drive selection and motor control. Regardless if IBM's drives had their logo molded into the front plastic, the technical reality is that they were and remain interchangeable with standard Shugart interface drives like the SA450. Peel the four wires that Shugart had previously added to create their 34-pin double-sided interface off the cable, and even getting an old 30-pin 1976 SA400 to work would have been merely a matter of software support.