Their last post was 2021-11-03 (https://news.ycombinator.com/threads?id=h1x) but a old archive of their profile from 2021-01-10 (https://web.archive.org/web/20210110145033/https://news.ycom...) shows that the text was already there, almost a year before their last post.
So yeah, seems they put it there themselves :)