Theoretically, maybe. But it is nearly impossible to come up with an implementation for Ruby, that is as performant as a compiled C program (and retains the characteristics of Ruby).
So, it is definitely true that it easier to compile some languages to fast machine or byte code than other languages. As a consequence, people will call Ruby slow, and C fast.
PyPy is getting there.
JIT, Runtime type detection and path optimization go a long way. And it's much easier to write correct Ruby than correct C.
When I went to college, the HP-41 was HP's top-of-the-line calculator and all the rich kids had them. I had a BASIC-programmable CASIO PB-700. In the end, I was able to finish tests in less time than it took the HP guys to program their calculators to spit the answer. I think it was the first time (1986 or so) I realized a more expressive programming language could be a decisive advantage over your competition.
No, it isn't. C may be spartan, but its failure modes are predictable and manageable. A ruby program can be incorrect for a host of reasons completely unrelated to the program (interpreter bugs, garbage collection problems, etc.) and the language as a whole provides features (dynamic typing, method injection, exceptions) that make it harder to write correct programs.
Ruby may make it easier to write programs, but it definitely doesn't make it easier correct programs.
...on some be benchmarks. It's not near the stage when it beats C or C++ in general.
And it's much easier to write correct Ruby than correct C.
C is not very type safe, but there are languages that are and have comparable performance to C (Ada, C++, etc.).