This advice seems exclusive to applicants with MAs. I don't think applicants out of undergrad are expected to namedrop dozens of contemporary academics and demonstrate in-depth understandings of the contemporary politics of subfields that interest them.
You of course have to read some work by POIs and frame your interests in a way that demonstrates fit with a program, but you also have to demonstrate individual intellectual ability/development/vision. PhD programs are professional development programs - I don't think committees expect (or even want) people to arrive pre-professionalized.