I can see why that's the case, given that Rust is that much more popular than Zig. I wonder whether there's a difference between LLMs reading code and writing. If reading code is easier than writing it, then it makes sense that Claude was able to port from Zig to Rust with good results.
Aside from relative lack of examples, Zig also changes fundamentally from version to version.
LLMs are fundamentally pattern recognizers though. Bun is big with lots of repeated conventions - very straight forward to translate those conventions to others (zig to rust)
I’ve been building a toy game engine for learning and have had great success translating small C libs (collision detection and physics for instance) into zig, often in one shot.