You get a bonus point of Starforce when you block an attack, and another bonus point if the blocked attack does 0 damage. Since Hollow Howlers tend to die around the time they deal 0 damage, that's probably the explanation.
I should probably include this information somewhere. Starforce has a lot of mechanics behind it, and an explanation of them would probably be in order. Just gotta figure out where to put it so that people know where it is...