The author suggests studying Programming Pearls. Bentley wrote there:

As soon as we settled on the problem to be solved, I ran to my nearest copy of Knuth's _Seminumerical Algorithms_ (having copies of Knuth's three volumes both at home and at work has been well worth the investment). Because I had studied the book carefully a decade earlier, I vaguely recalled that it contained several algorithms for problems like this. After spending a few minutes considering several possible designs that we'll study shortly, I realized that Algorithm S in Knuth's Section 3.4.2 was the ideal solution to my problem.

Why is vaguely recalling an algorithm studied years prior and needing to look it up indicative of a poor candidate in an interview?