Most cryptanalytic advances occur in tiny baby steps; there's rarely a big break that entirely lowers a long-standing problem from hard to not-hard.

Even when this occurs, the earliest iterations of these algorithms are intensely technical, and very slow. Of course, followup research often rapidly improves on these numbers, but that usually happens in collaboration with other authors.

So all-in-all, it is unlikely that a lone genius comes up with an efficient factoring algorithm all by themselves.