Unfortunately, they didn't tell us anything about how they did the codeforces test. It sounds like they just tried zero-shot, had GPT-4 see the problem and immediately write code to solve it. But that's not humans solve codeforces problems, we sit down and think through the problem. In a more real world scenario, I think GPT-4 would do way better at codeforces. Still not as good as a human, but definitely way better than their test.