I think the point is that an “open source project” is more than just the code and license, it’s also the community that builds and maintains it.
A fast rewrite of Bun in Rust has effectively alienated most of the people in the Bun community, so in that sense the “open source project” has died. It’s no longer a community project, it’s just become a personal project again.
A reset is very different from not being open source any more. If losing most of the community would mark a project dead in open source terms, then every new project would be dead on arrival. And that would just be silly.
Just so everyone know, Bun is and has always been owned by a YC funded org with full time employees. The overwhelming majority of commits came from them.