Very tragic, thoughts and prayers to his family and friends.
While it seems hard to understand how it could happen, it could be that he was focused on a vehicle approaching from the other direction. Unfortunately more than once when I've approached a stop sign and I see a car to the left or right, I tend to focus on that car, and after I've gone thru the intersection I realize I did not really look the other way (or don't remember looking the other way). I've realized this about myself so now I give myself a little "both ways" self talk as I approach. Too easy for a few moments distraction to lead to a really bad outcome.
Ride safe everyone!