You do realize that regardless of what was in the training data, the final solution included insights no human before had known, right? I share the same concerns regarding academic integrity but it would take a lot of motivated thinking to conclude that what the AI system did was not significant.
As far as I can tell (and my research was on the simulation side of Navier Stokes) the key AI output was a specific counter-example solution, generated with a method suspiciously close to that developed by the research duo involved in the controversy, a method that was discussed with Codex. So to me that insight is as insightful as the next undiscovered prime.