They won't open source it because the rust code is very likely a joke. They are proud of just using two dependencies, don't know that their "statically generated" stuff is actually called server side rendering and are hosting this stuff on a fuckin laptop.
It's probably a project that will teach them a lot. But in practice their implementation is worthless to everybody else because they are obviously completely inexperienced.
That said, that project is likely not worthless to them because they will probably learn a ton of stuff why it's hard to build a search engine.