Jackson's timer knew Jackson.
A little known fact about that time: It was done by none other than Red "Thumb Gun" Lewis. He and Jackson had a special relationship growing up together but this was what he called, "the greatest moment of my life".
Red had amazing reflexes and extraordinary dexterity in his fingers and thumbs. His favorite moment of friendship came about over video games. According to Red, "Bo done lost his mind gettin' his ass whooped in some Mario and Duck Hunt. I ain't never seen nobody get turnt over some laughin' ass dog."
But Bo didn't let that come between them. If anything, it strengthened their developing bond. They ran track together, though Red wasn't very fast. Because he never ran deep at meets, he was usually in the side of the track, cheering Bo on. Until he started timing him. And he made an art of it. He was able to not only perfectly anticipate Bo's start, but got down the rhythm of Bo's sprint and was able to perfectly hit Bo's last effort lean into the line down to .04 seconds. They worked as a machine on a cadence based on physical cues.
So there you have it.
Gif of end of race - Red on right