I had the same reaction as you when I heard it the first time - I never thought one person could make all those sounds on the guitar AND sing. And if you listen you will hear that the singing melodic line is a completely different rhythmic feel from the guitar riff. How he syncs the two of them together is beyond me.

But I know it is possible, and not dubbed at all because I've seen and heard my own son do it as part of his repertoire now...