He was only disappointed for missing the goal, you have to understand the excitement of this moment, he was just a few inches away from scoring this.
And when the ball passed over his head, he was naturally disappointed, i believe that he was surprised and took a few moments to realize that Treze was there behind him, standing at the right place and scored that goal for him.
When he saw the ball on the net and jubilant Treze running, he ran after him and hugged him!
Hopefully he will soon score too and become whole again.
He was altruist at times and no one can really blame him for putting himself over the team.
When DP faced a similar scoring crisis, he was much more frustrated than that and it showed...