Since he's probably too modest to mention it himself, the user you're replying to is the founder of the news aggregator and forum site Tildes [1] which is pretty much the gold standard of modern forum site design imho. If anyone has the right to make this comment it's him.
I think they were just talking about the design. HN is certainly a lot more active and successful overall, but it's extremely minimal for both design and functionality (which is part of its appeal).
Tildes's design has a lot more to it, including better responsiveness for mobile use, a built-in theme system with multiple themes (including dark ones), full markdown (CommonMark/"GitHub Flavored Markdown") support, syntax highlighting for code, etc. There are lots of aspects of it that would be nice to have on HN.
Thanks! I'm honestly a pretty terrible designer overall and there's still a lot that's bad about Tildes's design, but it's slowly improving. There are some major changes coming soon, and hopefully those will help some more too.
Definitely (open for anyone else too) - there's no messaging on HN though, so just send me an email to the address in the announcement post: https://blog.tildes.net/announcing-tildes
[1] https://tildes.net