They haven't fumbled anything. One person has used AI to vibe code a rewrite of a Zig program in another language. Zig didn't gain popularity due to Bun, last I checked Bun doesn't even mention it is written in Zig on the homepage. Zig is appreciate for major improvements over C, while being simple and concise.

In addition, a core Zig developer has explained why the PR was rejected, because it would introduce non-deterministic bugs into the compiler, just to achieve a speedup Zig is already gaining thanks to recent work on the self-hosted backend and incremental compilation, which are far more general as well.