check in which panel Oda decide to say who is the victor in that fight:
Zoro is conscious, still in the air ready to proper back to Onigashima.
Look where Oda decided to put the buble for the winner between QvS, right after he fainted and you can see the full sequence.
One fainted right after the fight, the other not. Simple as that.
In 1 case we see the character dropping to the ground, in the other not.