The fact that he capitalized both Cs indicates he's talking about the book, which is famous enough that I learned about it and its influence when I was in schoo

The fact that he capitalized both Cs indicates he's talking about the book, which is famous enough that I learned about it and its influence when I was in school ~15 years ago. GP wrote clean code (lowercase) which most people would take to mean the general practices of hygenic, well maintained code.