Fiora W - Negating Damage but still giving kill if executed by turret

In a situation where I was and we three-man dove a , I took turret aggro and riposted all of 's damage to me. In the death recap, it says only the turret dealt damage to me, and in the replay it is evident that none of his damage went through. But when I died to turret after killing him, it still gave the kill. Is that how it is supposed to work? I don't see how he'd get the assist as he technically did not contribute to the kill at all.