Not meant to be insulting or disparaging but I'm curious: Does Knuth have some form of highly functional autism or related? His body language is very weird to me. Staring at the floor a lot, seems to be lost in thought, etc.?
The man built a career out of thinking and you bring up the oddity of him getting "lost in thought"? He might have some sort of cognitive abnormality, but at this point who cares what it is? He's Donald freaking Knuth.
I know. I get that. I love the man and his work. He's one of the hardest working intellectuals I've seen and his contributions to computer science are of the highest order.