There was a reason why Roan called the Alpha Wolf's attention with those words. He wanted it to look at him! With that, the Alpha Wolf quickly looked to the sky. Just in time to see two kids slashing down their swords against it.
Back when the twins smashed the ground, the dust and dirt flew tens of meters in the air. Right after, Rean and Roan used the Fourth Form of the Death Style, Soaring Dragon. But this time, it didn't have a target; they used it solely to jump high in the sky.
If the Alpha Wolf wanted to see Rean and Roan coming out of the dust cloud, it would need to look far above its line of vision. But it didn't, and that's why it didn't notice them until the last moment.
'Death Style, Third Form, Three Claws of the Dragon!'