Unfortunately both rider and driver made errors at the same point in time. Had either of them altered or changed what they did at that moment in time it may have had a different outcome.
Without doubt the driver didn't look well enough and ensure the road was clear, for whatever reason didn't look properly on the day and will have to live with the consequences. I suspect those actions will be with him for a lifetime. He also pleaded guilty
“Benjamin Austin, the driver of the vehicle that struck David Holmes, ultimately pleaded guilty to causing a death by careless driving. He was subsequently ordered to perform 130 hours of unpaid work. His driver’s license was also suspended for 18 months.”
That said, if that was riders the normal riding style I'm surprised he's lasted as long as he did. It’s one thing saying the driver didn’t look properly, but it's also about giving yourself and other road users chance to see and react to you.
100mph on the approach to junction and then into it, is almost like having a death wish. How you can watch that video and not think that his speed was not a contributing factor is beyond me. You're not only gambling with your life but the lives other road users when it goes badly wrong at those sorts of speeds. Approaching a junction at that speed, It’s not beyond the realms of possibility that even if he had seen him, he may not have appreciated just how quickly he was going.
Would he have died had he been doing the legal limit? Who can say, you can do all the calculations after the event you like. What we do know is that he'd have had more time to react, as would the driver. He might have given himself a chance and enough time and distance to avoid or lessen the impact with the vehicle.
Both are guilty and it’s very sad that the chap lost his life. Fair play to his mother for allowing the footage to be used to encourage discussion and get people thinking and talking about it. Must have been a tough decision.