That is a very generous interpretation considering the lead in to the claim that I quoted is:

> "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).

It's not very generous, but actually plausible. Maybe your memory doesn't mix up objects (?), but other people's memories certainly does. (There is even a verb for it: mix up.) HN and reddit are basically the same, and it is very plausible that they got mixed up, and the rest is just derived.