[renhanxue]

I mean, for the most part the book is an edited transcription of what he said at the lectures (or, in some cases, what a guest lecturer said). But the lectures weren't scripted, and we know this because his lecture notes are preserved[0] and they do not contain anything like he full text of even a single lecture. They're just lecture notes, not a script. And of course, the book also contain a lot of example problems and graphics - those are mostly the work of Bob Leighton, I believe. There's a reason the book has had so many errata corrected over the years: it was never written and edited in the way a book manuscript would've been written and edited.

[0]: https://www.feynmanlectures.caltech.edu/Notes.html

[DiogenesKynikos]

Now your complaint is that Feynman didn't literally write down every single word he was going to say? He prepared more than 600 pages of notes and then delivered hundreds of hours of lectures. They were transcribed and published as a book, with normal editing. Feynman is the primary author of that book, for good reason.