its tuned down, there are actually 3 different versions of this song. Its either sounding out of tune for you because the play it a step down since suck it and see, or because bot Alex and Jamehhh messes up. The riff part is easy so its mostly Alex messing up with the twangy strumming, I think he can't really decide which way he wants to play, more downstrokes like in the fwnm version, or more twangy like the suck it and see sound. It has nothing to do with delay, since there is no delay (no slap either, its spring reverb infact) on the guitars in this song, only in the 2 verse on Jamies. hope that helps you