The author didn't do any of that. They ran each model once on each of 13 (so far) problems and then they chose to highlight the results for the 12th problem. That's not even p-hacking, because they didn't stop to think about p-values in the first place.
LLM quality is highly variable across runs, so running each model once tells you about as much about which one is better as flipping two coins once and having one come up heads and the other tails tells you about whether one of them is more biased than the other.