Julio Cesar comes out of his goal to win the ball and misses. The ball goes off Felipe Melo's head and into his own goal.
I think you have to blame both Melo and Cesar. Perhaps more blame should go to Cesar. Who, as goalkeeper, if he comes out for a cross, has to get a good touch on the ball, either punching the ball away or catching it. However, for Melo, he could have just tried to clear the ball away. There must have been some confusion between the two, one calling for it and the other not hearing the call.
Wesley Sneijder does a Diego Maradona and races to celebrate directly into the TV camera as it was his cross that went into the back of the net. It was a dangerous and well whipped in cross, so Sneijder does deserve to celebrate.