He says that he gets asked about this story and he met both Jobs and Gates only a few times and that in each case he was more impressed by them than they were of him.
The story is definitely false because Knuth is a very polite and modest person who has never been the sort of person that says "you're full of shit" to anyone.
More conclusively, another person in this thread pointed to the letter from Knuth in his own handwriting in which he says the Jobs story is untrue:
http://markharrison.net/stackoverflow/knuth/knuth-page2-enla...