It reminds me of the USB keyboard extender that came with old Macs. There’s a little notch in the socket so you can only use it with Apple keyboards. At the time I thought it was a petty way of preventing you from using it with any other device, but apparently the reason they didn’t want you to use it with other devices is because the cable didn’t comply with the USB spec.
Yes, USB extenders are not spec-legal (because the device isn't built expecting to be extended).
But you can have an extension cord which accepts USB on one end but doesn't accept USB on the other.
So the keyboard has a superset connector so that it can go in regular USB and notched USB, because it is verified to work right when using the extension cord.
This design also means you can't plug one extension cord into another to get an even longer distance (which the keyboard wouldn't expect). Pretty clever solution.
Some pictures here: https://www.reddit.com/r/assholedesign/comments/b1u08k/this_...