With Rust, a panic occurs right away when the fuzzer develops input that performs e.g. out of bounds access. With C, it's possible to go wrong a little but not enough to segfault or to go wrong enough that by accident the access looks valid (for an unintended valid memory address) to a sanitizer.

In that sense, fuzzing Rust is more certain to make the bad things actually be caught than with C where there's a chance that the fuzzer developed input that caused UB but the UB didn't happen to be caught by the mechanisms that are supposed to discover bad events during fuzzing.