Alright, I noticed a bug like that in the main game too.
The idea is that among the sheep there are fake ones that are in reality wolves which give you a penalty if you bring them to the eye instead of getting you closer to the goal.
These fake sheep either have pointed ears or a slightly different headshape.
You are right though in that the tutorial doesnt really explain this mechanic. (Sry again)
Hope that clears your confusion.
If this was actually a bug and you brought a normal sheep I'm extra sorry -_-