I think his point is that if you write normal single threaded code then your other cores are going to be idle. But if you write in a high level JITed GCd language then the other cores will be busy making your main thread run faster by profiling it, recompiling it with risky optimisations, clearing garbage asynchronously and so on.
You can't just take advantage of SIMD, hyperthreading, multicore, or large caches without writing code in a way that takes advantage of that even at a high level. Some things can be faster when compiled at runtime but everything is a trade off.
But ultimately I believe that C is fast mostly due to manual memory management but that's not a trade-off I'd take for most tasks.