From what i understand he has a knowledge of CS, but didnt delve into code at apple. From Mortiz' book, I can tell he did write code for Atari.
"You're full of shit," Knuth responded.
http://folklore.org/StoryView.py?story=Close_Encounters_of_t...
[edited to add: I should of course just have called it "unknuth", but my pun-sense wasn't quick enough on the mark.]