He had trouble keeping his eyes open squinting.
So he totally missed the rocks.
Clear to see by the shadow longer than his height straight behind him .
He was experiencing disabling or blinding glare.
Very high chance this would have been avoided while wearing a good pair of polarized sunglasses.
Certain wind directions will make you ride on one tack directly into the sun.
Especially bad when the bright sun is at a 45 degree or less.
The lower the sun is to the horizon the higher the glare from the sun and water reflection can be.
Think when you drive your car directly into the sun early in the morning after sunrise and late in the afternoon before sunset.
You have to use the sun visor and majority of people also wear a good pair of driving polarized sunglasses.
Sun glare reflects off the car hood and dashboard and after a rain off the pavement.
It has been proven that many car accidents and hitting people could have been prevented with polarized lenses.