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.