”Zig builds C faster than most C compilers” is a nonsense statement, which I don’t know how to answer.
The fact is simply that despite Zig uses LLVM as a backend in the same way Odin and C3 does, it compiles much slower. Exactly why that is, is something I can only guess at, but the fact is that Zig cached is still much slower to compile than Odin or C3.
(There are a few possible candidates as to why this is so that I identified and can share if it is interesting)
In any case, Zig is only ”fast to compile” if you compare to the triad of infamously slow languages: Swift, C++ and Rust.
Anything else is just hype.