The claim is "fast as C", so I was surprised that the performance comparison was with Ruby, not with C. On my machine, the Ruby Fibonacci program executes in 47.5s, while a corresponding C program executes in 0.88s - that's a factor 54 difference, while the article reports a factor 35 for Crystal. That's good, but what causes the difference? This benchmark is pretty much all function call overhead, so I doubt it's representative of real performance-sensitive code.
The Crystal website itself makes a more modest claim than "fast as C" under its language goals: "Compile to efficient native code", which it clearly does.
The Crystal website itself makes a more modest claim than "fast as C" under its language goals: "Compile to efficient native code", which it clearly does.