Bizarre. How do people make such big, splashy findings that can mess with people’s sense of optimism about science and innovation, without doing the simplest types of checks on their data and methodology.
No, the question is: how did peer review not catch it? I have the impression that reviewers don't have the time or incentive to give papers more that a cursory review. Independent of this case, a great many papers are published where the only "proof" is a user study or survey with an extremely low number of participants, but it still gets published. Many papers don't publish their datasets and don't contain enough detail to try and replicate their results.
There should be a real incentive/compensation for reviewing properly and real consequences if a paper gets retracted for reasons that should have been caught in review.
In this case it's fortunate that it did get found out in the end.