They tested it on problems from recent contests. The implication being: the statements and solutions to these problems were not available when the Github training set was collected.
From the paper [0]: "Our pre-training dataset is based on a snapshot of selected public GitHub repositories taken on 2021/07/14" and "Following our GitHub pre-training dataset snapshot date, all training data in CodeContests was publicly released on or before 2021/07/14. Validation problems appeared between 2021/07/15 and 2021/09/20, and the test set contains problems published after 2021/09/21. This temporal split means that only information humans could have seen is available for training the model."
At the very least, even if some of these problems had been solved exactly before, you still need to go from "all of the code in Github" + "natural language description of the problem" to "picking the correct code snippet that solves the problem". Doesn't seem trivial to me.
> I don't believe it would be difficult for a human to solve problems on Codeforces when given access to the entirety of Github (indexed and efficiently searchable).
And yet, many humans who participate in these contests are unable to do so (although I guess the issue here is that Github is not properly indexed and searchable for humans?).
[0] https://storage.googleapis.com/deepmind-media/AlphaCode/comp...