As others have noted, that is probably a Code 0 or Spinnaker halyard. 2:1 purchase does not make sense for a genoa (IMO it does not make sense for a Code 0 or Spinnaker either, but that is certainly debatable..).
The twist however was likely due to having a fixed snap shackle on the halyard, rather than a conventional one with the swivel.
This is actually an interesting dilemma: with a
furling Code 0, if you have the shackle with the swivel, the Code 0 is likely to become undone (not much, but enough to be a real pain) once furled.
If you change to the fixed shackle, the Code 0 does not unfurl on its own, but then if you use that halyard for the spinnaker, since the shackle does not swivel, the halyard is likely to twist and get stuck somewhere.
Not sure there is a solution to achieve both... Any thoughts?