I think that when Frank points out that Hip-Hop, is not folk music "although there are some aspects of this music that hark back to earlier roots", he is making an important point--

There are many aspects of folk music that are reflected in, repeated in, or even used as the basis for other kinds of music--

People tend to generalize, and refer to anything that includes one or more elements of folk music(such as instrumentation, melody, text, repertoire, or performance style) as folk music--a lot of times simply because there is no other accessible name for it--

Frank's point, which I finally get, is that even when the music is created and performed within a certain cultural context, the music has to be passed through consecutive generations in that culture to be tradtional or folk music--