Looking at the two crashes it seems they took place at the same location. From the camera angle, the crashes were either at the top of a rise or the beginning of a downhill run to the finish, the point of gear shifting. With that many riders in close quarters all it takes is one missed shift or dropped chain and the rider behind is into someone's wheel. It is good news that no one was hurt very bad.
I was in a Cat 4 race two weekends ago that was held in rain and wind on country roads simular to the images. We worked hard each lap to split the field and eventually got it down to around 12 riders with 4 miles to go. Going up a roller into the wind a rider attacked and just at the top of the roller he pulled his foot out of the pedal. He shot across the front of the group and two other guys went down with him. I got through fine, and I guess because it's racing my thoughts were, "too bad for those guys" then took advantage of the chaos to make my own attack to get away. We ended up with 6 riders getting away and dropped one making a 5 man sprint for the win.