One is being open about the fact that you're ending the fight because it's no longer interesting, the other is being deceptive. Whether being deceptive is good or bad is a personal opinion, I personally try to avoid it.I myself don't find any appreciable difference between "calling it" and fudging. In both cases the DM is just choosing to no longer play the board game as per the rules of said game. So one isn't any better or worse than the other to me.