Cocoa in a tasting note means the smoke reminded the taster of chocolate, cocoa powder, or cacao husk. It is often noticed in cigars with maduro wrappers and in some leaf that has been fermented longer. This is a common association, not proof of anything. No cocoa is added to the filler.
The word has its ordinary English meaning, and this encyclopedia does not use a long list of dessert words to describe cigars. If a reviewer thinks a cigar tastes like chocolate, the review simply says so.
Related glossary entries: earth, leather, strength vs body.