A "very small, nearly healed cut that didn't completely form a scab" does not constitute an open wound. An open wound is a large, deep wound in which blood is actively pouring out, and would probably require medical attention and stitches. You did not have a risk from this scenario. Relax :)
One final question: so, why are there so many reports out there that hiv can be transmitted via open wound? Are there exceptions?
May I ask why? And would it make a difference if the scab didn't form completely over the cut?