I don't believe the author is claiming that C is obsolete; nor do I believe he is claiming that no one knows C. What I do think he's implying, if not outright

I don't believe the author is claiming that C is obsolete; nor do I believe he is claiming that no one knows C. What I do think he's implying, if not outright claiming, is that there are many people who grossly overestimate their knowledge of the language. That doesn't mean there aren't a lot of very talented and knowledgeable C programmers— but there are a lot of people out there who think they're hot shit because they've done all the exercises in K&R, but who have no real familiarity with the formal semantics of standard C.