It's worth noting that they are using bluesky feeds and moderation services/labellers. They just have written their own rust implementations for the tools/services and their frontend (which is largely a fork of bluesky-social upstream) changes the default experience/settings.

So there's still full interop. You can use the blacksky feed and labeller from other bluesky apps and likewise for the reverse.

TLDR: They wrote their own implementation of the tooling in their language of choice (Rust instead of Go) and their version of the "app"/frontend sets the defaults for their community.