Depends. (As everything always does.) “Carbon fiber” literally means just the black threads, in English as in any language. When you say “This bicycle / fishing rod / automobile part is made of carbon fiber”, what you _actually mean_ is that it's made from carbon fiber- reinforced polymer (=“plastic”). Stuff isn't built from _just_ the fibers; the plastic needs to be there to keep them together / they're just there to reinforce the plastic (or both).

The GP (G-G-G...P?) post seemed to be using the shorter expression, but as a shorthand for the longer (as most people do) in English but not in German, which may have caused some confusion.

But it's the same in both (all) languages: The shorter expression technically means just the reinforcing fibers; the actual material used to make stuff is technically called the longer expression; but in ordinary usage most people use the shorter expression to mean the longer one.

My German-as-second-language understanding is:

Kohlenstofffaserverstärkter Kunststoff == Kohlen (literally coal but understood more broadly as any carbon) stoff (material) faser (thread) verstärkter (reinforced) Kunststoff (plastic).