I was basically working from memory on this, so I went back to watch again. The defender (Ibarra) doesn't push Segal from behind, but there is substantial contact between him. Basically, Ibarra throws himself forward and in the process traps Segal's left leg between his two legs. Segal then sticks out his right leg to try and get to the ball. Segal's right thigh then contacts Guzan's knee. So, Ibarra doesn't cause the contact between the Segal and Guzan, but he definitely affects Segal's trajectory and perhaps makes the contact worse. As mentioned, a foul call on Segal would be the right result, but there shouldn't be a card.