DQ seems justified to me, albeit based on fewer watchings than the race jury. Sagan had plenty of room on his left. If he had stuck to his line, Cav would have had room. Instead, Sagan moved to his left, and flicked his elbow at Cav. Sagan was also apparently being similarly irresponsible yesterday.
That said, it seems like Cav has pulled similar stunts in the past, no?