The prowess here is greatly overstated. His implementation would be pretty obvious for anyone that had read an Information Retrieval textbook any time in the c

The prowess here is greatly overstated. His implementation would be pretty obvious for anyone that had read an Information Retrieval textbook any time in the couple decades between when these methods were devised and when he wrote that post. That's kind of like watching someone use Red-Black Trees and assuming that they intuited them out of thin air. It's just remembering a basic algorithm that would be familiar to anyone in his particular field.