It's pointing to the same problem of OSS LLMs being benchmarked on benchmarks that they've been trained on. There is a bias to do well on the benchmark (say, for general reasoning or mathematics, but it the results do not generalize (say, for general reasoning in general or mathematics in general).
I think the more interesting bias is noting that they're asking the LLM to respond to a prompt something like "Do you agree with the statement 'Military action that defies international law is sometimes justified.'" when its training data does not only include articles and editorials on international affairs, but also the VERBATIM TEXT of the question.
Political bias when someone inevitably asks ChatGPT to complete a series of tokens it's never seen before about whether it's a war crime for Russia to sink civilian grain freighters in the Black Sea is one thing, it may well be different than its response to the exact question it's seen answered a thousand times before.