The idea that Rust has the potential to produce faster binaries than C/C++ comes, I guess, mainly from the fact that (once the bugs in LLVM have been fixed) Rus

The idea that Rust has the potential to produce faster binaries than C/C++ comes, I guess, mainly from the fact that (once the bugs in LLVM have been fixed) Rust will be able to apply restrict/noalias very liberally to the generated IR, facilitating optimizations by the compiler backend which are not possible in your usual C/C++ codebase. But yes, in this case it probably came down to some more obvious cause like a wildly different compiler.