It's "the content that people interacted with that they formed an opinion on "Richard Feynman" from was actually editorialized and published by other people"
They're not trying to take credit from Feynman, theyre trying to divorce the character of "Feynman" as written by these authors from the real historical person
So again, I think "never wrote a book" is misleading if it gives the impression that the portrayal of Feynman in such books was not Feynman's own portrayal of himself. It was.
With some more thought, the fact that he wasn't the direct author of any books is interesting but not really that significant to his character, so i can't see much reason to point it out other than to discredit his achievements.
Though if the achievement being discredited is the number of books he's seemingly written then it makes sense to a degree.
Only if you take "written" literally, as in, he didn't do the actual writing, he just told the stories orally and someone else wrote them down.
I personally don't care much about that; the stories are his (including, as I've said, whatever misrepresentations of what actually happened they contain). Lots of people have books ghostwritten, and that's not considered unusual.
More than that, there are famous examples of books for which someone got the credit for the writing when they actually did little or none of it: John F. Kennedy being credited as the author of Profiles in Courage, for example. Even the content of Profiles in Courage was probably less Kennedy's than the content of the books Feynman gets credited for was Feynman's.
But the statement "never wrote a book", without a lot of context (which might be in the video or Gleick's biography, but wasn't in the post I responded to), suggests that Feynman didn't create the content that's in the books, but someone else did and Feynman took credit for them. That is emphatically not the case. All of the content of those books is Feynman's. Leighton took Feynman's content, delivered orally, and put it into publishable book form. Certainly not a negligible task, and he deserves credit for it, but it doesn't mean the books aren't Feynman's content. They are. And nobody, certainly not Leighton, ever said otherwise.