I think most professional programmers get stuck in "blocking" operations (wait for requirements, wait for consensus on design details, wait for feedback, wait for some other developer) which limits their raw coding productivity and those that try to push past these blocks quickly start trading coding productivity for quality.
The SoC programmers on the other hand generally have all the big blocking operations taken care of ahead of time by the SoC managers and mentors, allowing them to focus just on the coding.
If you were doing Agile (and therefore had a reasonable metric of the relative size of each requirement), then a better metric might be your personal "velocity" of completed user stories, divided by the estimate amount.
I think a really cool metric would be who has the fewest lines of code per completed user story.
Somehow that story seems to fall short of it's possibilities. What programming languages have been used, for example - maybe the 20000 lines people where Java developers and the 4000 lines people where lisp programmers (or whatever)? And the argument for measuring the productivity by lines of code wasn't really made in the article, it just says it is a bad measure and then goes on to judge everything by that measure.
How long is the summer anyway, three months? So 20000 lines could be about 200 lines per day?
The article says that because the mentors found the project work acceptable, then lines of code becomes a good measure of productivity, even though it generally wouldn't be. But I think it's still a bad measure of productivity.
In fact, I think the lesser amount of code for the same size project is more productive. I'd prefer the programmer who can meet the project goals in 4,000 lines of code over the one who does it in 20,000 lines. Given those two numbers, I can't help but feel that the 20,000 lines is spaghetti code. (I realize this in my own prejudice and it may not be the case.)
As Antoine de Saint Exupery says: "Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away."
Going for perfection, in most cases, is probably not the most productive use of time. But I think this quote is still generally true for programming.
The SoC programmers on the other hand generally have all the big blocking operations taken care of ahead of time by the SoC managers and mentors, allowing them to focus just on the coding.