Common Lisp has more in common with Python and Ruby than Haskell. Perhaps you should study some of these languages before encouraging other people to.
Arguably, so does Scheme. My impression of Ruby is that it's sort of a bastard of Perl and Scheme.
More like Perl and SmallTalk.
Scheme is a bit more biased in favor of functional techniques though. Recursion (in the vast majority of cases CLers will just use (loop) instead of recursing), continuations...
I'm a heavy Common Lisp user, but I'm only casually familiar with Scheme, so I opted to leave deconstruction of that aspect to others--such as yourself!
Edit: I meant to say functional not pure functional. Blog post changed.
I question your qualification to advise people on interviews if your own theory knowledge tops out at "casually skimmed a wikipedia page."
He's making the distinction between saying a language is "functional" versus "pure functional." It is not correct to classify Lisp and Erlang as pure functional languages, because they both include support for imperative style programming.