"Of the 3,800 students in our classes (from 2000 to 2006), this study included only the 494 who used the C programming language and who also completed all 10 programming exercises."
So they started by discarding the bottom 3,300 students (the bottom 87%) and selected out only programmers who used C and who could complete all 10 assignments.
This right there that shows the "myth" isn't a myth. 87% of their students didn't even make it to the starting line for their study.
Second, they're studying students, not professionals. As anyone can tell you, someone who has been programming competently for a while is massively more productive than someone who has had one semester of college. So there's probably a much narrower range of ability if everyone is just now learning to program.
Third, their own data shows a 10x difference in performance between the top performers (who did it in 30 minutes) versus the bottom performers (who did it in 300).
Fourth, their challenges don't sound realistic. All 10 were just some i/o, some loops, and some if statements? I'm not sure that getting a narrow range of results really means anything, as they're testing just basic skills. Why not give them a day or two to develop both an interpreted language and an interpreter for it, like John Carmack did for Quake? What? You think nobody would be able to do it? Precisely the point. There are programmers who can just casually knock out something like that.
Fifth, their research runs counter to established research on the subject, so given the above flaws, it is really irritating to see the author (who is presumably a smart guy) calling it "The End to the Myth of Individual Programmer Productivity" is just anti-scientific hogwash.