> But the title of the post wasn't a Common Lisp ... it was a Lisp interpreter which technically Racket is a Lisp.

Common Lisp is Lisp: it's a standard which specifies the minimum required functionality of a Lisp implementation. Anything which doesn't meet that standard isn't Lisp.

Scheme, Racket, Hylang, Clojure may each be a Lisp, but none is Lisp (unless one of them has bothered to implement the Common Lisp standard).