This seems like a false dichotomy to me. The "shallow" character seems completely uninformed about the basics of computer science, maybe having worked through a C tutorial or two, while the "deep" character seems to have an encyclopedic knowledge of every C spec and compiler implementation that's ever been written. How many interview candidates really fall into one of those camps?

I don't really know C that well -- certainly nothing spec- or compiler-specific -- but I got "deep" answers for most of the questions just because I know that generally C compiles straight to machine instructions, and I know how computers work. (I got 5/5 on the little quiz, and the tutorial on sequence points was completely new to me.)

C isn't hard. Thinking like a computer, in any language, is hard. The ability to predict what code will do, while important, is less crucial than the ability to figure out what's really going on when you get one wrong. I feel like calling that ability "deep knowledge" is putting the cart before the horse.

To put it another way, "I don't know the answer to that question, but here's a guess" and "I know the answer to that question, here it is" are both less impressive answers than "I don't know the answer, but give me a second and I'll figure it out for you."

Or maybe I'm missing the point.