If the dad was inside the home, shooting through a doorway, and probably shooting through the closed or partially-open door, he may not have a good view of the invader, and stopped at three, when he perceived that the break-in had ceased.
If the dad DID have an unobstructed view of the invader, then, yes, of course, the simple factor of human reaction time applies. We can see that shooting is no longer necessary, but it takes a while for that to work its way through the assessment loop.
The you-tube video seems to have been taken down, but, based upon the one time I viewed it, that distinctive, prolonged blink, and that look in the invader’s eyes, after the blink, well, I cannot read minds, but if pure rage has a look, that was it.