My read is that they do what Volkswagen did with the emissions scandal: they detect when they're compiling code for the benchmark, and compile it in a way that makes the benchmark code (specifically) faster. That optimization wouldn't generalize to "real" code because the optimization relies on the specific code and data ("data" being fixed non-code inputs processed at runtime) being processed by the benchmark to have an effect. If you know based on prior knowledge that, for instance, code that uses a signed integer will always only handle positive integers, you might cheat by optimizing it to be unsigned integers. But a compiler couldn't possibly know that in advance because it can't see the data the code processes at compile time.
For your code to benefit, it would have to do the same things the benchmark is computing and have the same shape of data as the data included with the benchmark suite.