That's the way he likes to paint himself. From a lecture he gave at my university I remember that he said something along the lines of, that he usually came up with the idea and others wrote the code. From the experience out of the same lecture, however, I can tell you first hand that he knows his way around code and that he can code. The lecture was indeed more of a hands on workshop with Knuth spending most of the time in Emacs coding MMIXAL assembly - pretty low level stuff actually.