It is mentioned on section "Limitations and Bloopers" of the page [0]:
> Combining evolutionary optimization with LLMs is powerful but can also find ways to trick the verification sandbox. We are fortunate to have Twitter user @main_horse help test our CUDA kernels, to identify that The AI CUDA Engineer had found a way to “cheat”. The system had found a memory exploit in the evaluation code which, in a small percentage of cases, allowed it to avoid checking for correctness (...)