Not sure what you're going for here. If your question was "Did Peyton Manning play like garbage", you'd have a universal yes.
If your question is "Did Peyton Manning cost them the game", it's obviously a lot trickier because football involves so many players needing to do their job for team success. Collectively, the Broncos played terrible and Seahawks played great. Peyton Manning is the face of the failure (QB's get great credit/blame based on team performance), but it's not like he was solely holding them back from winning. They were outplayed everywhere.
If Peyton's performance was like Neil O'Donnell or Rex Grossman's Super Bowl performances where the team was holding on while the QB ruined their chances of winning, but Peyton wasn't receiving blame, you'd have a point. But like I said they were outplayed everywhere.