At first I thought it was brain slip in the HN title, then I saw TFA also said "clear", so thought it was perhaps a sarcastic jab at the original "clean" room story it is commenting on, but maybe in the end just an error ?
It would also be interesting to see how well the best open weights models such as Kimi K2.5 can do on a task like this with the same prompting to first gather specs, etc, etc.
In fact this would make for an interesting benchmark - writing entire non-trivial apps based on the same prompt. Each model might be expected to write and use it's own test cases, but then all could be judged based on a common set of test cases provided as part of the benchmark suite.
In any case, an interesting experiment.