Not "a" human's understanding; Humanity's understanding. Understanding the research problem, and the solution especially, is a lot more involved than simply "read their methods". That's the whole point being made.

It matters if a human came up with it because of everything mentioned in the article... A mathematician's solution is necessarily built on other's ideas that have been disseminated, internalized, pressure tested etc. Methodologies differ too. AI can abuse its compute resources and generate a true/false or counterexample statements, without laying the foundation that a decade of globalized research would have.