My thought on what happened:
The mission to get Osama Bin Laden did not go as planned, and a helicopter was shot down in the process of killing him (killing the 30 Americans). Then they stage a fake RPG attack that killed the SEALS that really died getting OBL. The reason to do this is that Obama didn't want another failed mission on his hands as President since he wants to get re-elected, so he staged the guys' deaths to make it look like an American war tragedy, and Obama can play Mr. Sad Guy.