Imagine telling Brian Kernighan about a cool language you found called C, not realizing Brian wrote a lot of C.

Imagine telling Dave Thomas about a cool language you found called Ruby, not realizing Dave has written a lot of Ruby.

Imagine telling Douglas Crockford about a cool language you found called JavaScript, not realizing Douglas has written a lot of JavaScript (much of it full of bad ideas, but that's irrelevant in this case).

Imagine telling Harold Abelson about a cool language you found called Scheme, not realizing Harold has written a lot of Scheme.

Imagine telling Randal Schwartz about a cool language you found called Perl, not realizing Randal has written a lot of Perl.

Like all of the above, for the respective language (LISP in Peter's case, C in Brian's, and so on), Peter Norvig is a well known master who has written a seminal work about the language.

q.v. Paradigms of AI Programming: Case Studies in Common Lisp

He also wrote Teach Yourself Programming In Ten Years, which many people who know basically nothing about LISPs have encountered and consider important.

If I would have any objection to the brief story's use of the term "ironic", it would be about the fact that many LISPers might not be as enthused about Clojure, so it's possible Peter hasn't really looked into it. Your question implied that Clojure is just "Lisp", though, and if we're talking about "Lisp" in a generic sense (i.e. the LISP family), I think Peter Norvig is one of those luminaries that everyone who pays attention to the social context and most important written works about LISP would know. I don't even pay that much attention to those aspects of LISP knowledge, and I know about him in the context of LISP.

That's not to say everyone who has an interest in LISP should be thought deficient for not knowing about Peter. It's fine if you haven't stumbled across him before. Sometimes, people just miss things that, in retrospect, might seem like something they should have known.

That doesn't mean you have to even have an interest in LISP.

This should, however, hopefully, give you a sense of why Peter might think it was "ironic", even if "ironic" feels a bit questionable as the appropriate choice of term there. I'm sure to him it felt a little ironic, and that makes sense to me as an emotional response, at least.

Does that help?

(Imagine telling William Shakespeare about the Renaissance era techniques of being a playwright, or telling James Cooke Brown about a conlang called Lojban. Of course, I suppose James might be dismissive of Lojban, given he tried to control Loglan by proprietary means after creating it, thus prompting others to reimplement it as Lojban, undermining his efforts at such control.)

edit: Note that I'm not saying there's anything wrong with someone not realizing one is speaking with a Big Name in LISP when meeting Peter Norvig. I'm just saying that Peter is perhaps justified in finding it a little "ironic", and jumping to conclusions about why he would feel that way (if that's what you're doing) might not be fair.

I would probably feel awkward in Peter's position. I've been in a similar position before, including once being told about a cool article that I actually wrote as if it would change my life, and I never know what to do in a case like that. How do you point it out without possibly making someone feel offended? Humans get offended at the silliest things sometimes, and I occasionally find it quite difficult to predict.