You're basically saying scientists can become good programmers if they become professional programmers. Of course they can be, and I doubt anyone would argue that. Some of the best programmers I know have zero college education at all, so of course it's possible for mathematicians and scientists to do the same.

But that isn't anywhere near the point of the article. It's talking about scientists that did NOT switch to writing software professionally, but continue to write it merely as a tool to accomplish their primary scientific goals.