Rust is just a better and more productive language than C (I guess this is a subjective statement, but obviously they would think so and I would agree with them).
Nobody ever claimed that it's impossible to write these drivers in C -- C is "Rust-complete" in the sense that you could in theory write a compiler that translates any Rust program to C.
They're just claiming that Rust allowed them to write much higher-quality code, much faster, which seems plausible.
