That is a brutal video.
People have missed seeing the checkered flag. People have mistakenly thought the last-lap flag was the checkered flag. It happens. Rider could be head-down paying attention to cutting drag, and not see what is going on up ahead.
This is why you don't ever slam on the brakes in a place that is not ordinarily a braking zone, no matter what. Checkered flag? Shut the throttle and coast down to 70% of racing speed and do your cool down lap at that pace. Red flag? Shut the throttle and coast and put your hand up and get off the racing line. If the distance that it takes to coast to a stop takes you past the marshal station then so be it, proceed to the next one, don't slam on the brakes. Broken bike? Get off the racing line and preferably off the track. Jockeying for position to be on your buddy's GoPro video camera? DON'T.
I came close to hitting someone on a broken-down bike on the back straight at Shannonville many years ago. In the midst of a huge pack, I couldn't see the actual broken-down bike on the left edge of the track. But I saw the riders in front of me all veer to the right, and I figured there must be a reason for it, so I did, too. Had I not done so, there would have been NO time to react before the collision. It was very close.