Cmwissy said:
It's the motion of how he's doing it - I could hold the handle of a knife and stab someone; But with the hidden blade he punches them with it between his knuckles.
I'm not talking about semantics - I'm talking about how he does the stabbing.
I always saw the assassination animation in AC2 as open palmed, but assuming I'm wrong I guess you could technically say that despite the way he uses the knife it is a stab ended with a punch.
When he assassinates someone he has the blade in between his knuckles, but the knife connects with them first, making it a stab. Then as the knife goes into the guy he will eventually hit them with his fist, making it a punch.