I am also in Iowa and I am sure of how I feel about this. The man is a hero and was right to shoot the perps, even if they were fleeing. A vehicle is a deadly weapon, particularly when being weilded by a criminal who has already shown he has a desire to kill you, as evidenced by his shooting you moments before.
The man needs a larger gun. If size is a consideration then he should get a pocket .40, Kahr makes nice ones. Maybe something in a Kel-Tec.
Like I said, I agree in theory, but would you be willing to go to jail? Because in Iowa, you likely would. That is the question.