I think behnamoh confused HN with Reddit, which was actually rewritten from Common Lisp to some other language (and the original Common Lisp version is still available in the source code form).
> "Hacker News was built in Arc, which is a Lisp"
and the follow-on is:
> HN is such a simple website by all metrics, and the fact that CL/Arc was dropped in favor of another language further confirms my belief that Lisp's days in industry are almost over.
He gets the right language for HN (Arc, still the language of the site), and not the Reddit language (CL as you point out, which was dropped for Python, and Arc was never used).