Vista got pushed back a little by the clash wave whereas Mihawk stayed still.
The Vivre Card also states Vista jumping Mihawk
despite knowing how powerful he is. If you use the anime as word of God, Mihawk asked Vista to show his fighting style to him, as if Mihawk's more interested in seeing this famous swordsman fights than slaying him.
Mihawk being the WSS and equal to Vista is a contradiction when you hav characters like Shanks who fight with swordsmanship, even if we go into no-true-swordsmanship territory.