They found an order of 10 productivity difference that showed up under any of a number of possible measures. The also found that the best predictor of a given person's productivity was the productivity of the other person from the same organization. They also identified a number of workplace environment issues that were strongly correlated with productivity.
This overall picture comes with many caveats. Individual productivity differences were still quite significant. They didn't have any way to tell correlation versus causation. (To what extent does a better environment make programmers better, versus correlate with being able to hire and retain them?) The coding assignments were fairly small. So don't read too much into the result.
But given the size of the difference, and that it is one of the few attempts to quantify these issues, it isn't a result to take lightly either.
I'm not sure I buy it for individuals, except in the limiting case of someone completely not knowing what they're doing and having no idea where to start.
I guess it's also possible with the economist's definition of productivity ($$$/hour), since so many projects turn out to be commercial flops. But by that definition, startups and research are some of the least productive sectors of the economy, not the most.