If the hypothetical driver wasn’t speeding, he would have more time to see the walker up ahead, presumably.
As for the article, no telling with these particular ding dongs, who hit him and then went on their merry way.
A motorist travelling at 5,280 feet per minute/88 feet per second is going to be hard-pressed to react to someone walking 3.5 MPH on the road in time to avoid striking him.
(In a residential neighborhood with a 25 MPH speed limit, we might tell people to drive cautiously. On an interstate with a 60 MPH speed limit, we can only tell people to stay off the road.)