Um, actually, I think it's the other way around. The fact that he wasn't 'comprehensively beaten' by his team mate might have been the cause for his disappointment. He pretty much stuck with Vettel throughout the race, so he knew he had the pace to beat him if he'd had been leading, making the mistake at the start that much more costly. I believe that was the face of a man who should have won the race, and knew he should have, but took the first corner too easy and blew it.