I think the point, the author maybe didn't intend it as such, is that Lisp generally encourages the creation of many domain specific languages. You have the too

I think the point, the author maybe didn't intend it as such, is that Lisp generally encourages the creation of many domain specific languages. You have the tools to fundamental define completely new language abstractions that feel very much like first class constructs both syntactic and procedural. The comment about C++ is probably mostly for the edge factor but if i was to try to delineate what is different about C++ melting pot vs Common Lisp it would probably be the homoiconicity of CL which for the most part allows far more seamless integration at the syntactic level whereas C++ is required to include an ever increasing and bewildering array of differing syntax constructs.