The Torment description is incredibly ambiguous, but the way I interpret it/have seen it interpreted is as follows:
- You can't use the same move two times in a row
- You can't use any moves you used in the previous round
That means the only move Joltik couldn't use was Bug Bite, being the only thing it used/tried to use in the previous round. Now for the remaining action of torment it couldn't use Cross Poison or Poison Jab. Even though it had already used Poison Jab, it wasn't in the round prior and hence wasn't limited by Torment.
Plus, you're about to kill the poor bug anyway.