It's within 5-10% on average, sometimes faster, usually a little slower, very rarely slower by much. The person you're responding to said "approximately". I feel like this is needless pedantry.
Rust also allows you to make architectural decisions in the name of performance that would be completely unmaintainable in C. See: the Servo project.
Further, it should be possible for Rust to eventually reach a state where it's faster than C because of the lack of pointer aliasing. This opens up a whole host of optimization opportunities, allowing it to get closer in performance to Fortran (which is intrinsically the fastest of the bunch).
Rust also allows you to make architectural decisions in the name of performance that would be completely unmaintainable in C. See: the Servo project.