I've played all the way through the campaign on Veteran, and I went back and got all the campaign achievements and located all the intel. However, on the main menu screen, the game tells me I'm 100.3% complete with the campaign.
Having a percentage higher than 100% is normal in things like the Multiplayer component, where it gives you a percentage based on how far along you are in the prestige track (so you have 100% at level 80, and then 200% at level 80 first prestige, 300% at level 80 second prestige, etc) but I don't understand why I have exactly this percentage for the single player.