This statement is quite unfair. I have read the code from Mongrel2 and I've learned things which completely eluded me in the past. Have you considered that he is actually a human being which can be surprised at how an old book can present aspects never noted before?
Just because he hadn't thought about that particular language horror side effect doesn't mean he doesn't understand C. C can be manipulated in horrific ways, such as a psychopath can absolutely horrify you. That doesn't mean you don't understand life for example.
And no, he doesn't mock people who read the standard. The discussion was entirely about something else. He proposed an improvement on how to handle strings and how the original K&R code should only be looked at from a didactic POV and not production level quality.
That is what I saw in that thread.