>This doesn't seem to be easy.
Quite agreed. It's not an easy thing to measure accurately. I believe the explanation for the numbers is indeed the first of the two options you present, as I wrote in the original piece. As the Dr. Dobb's readership has grown vs. 2010, both in terms of unique visitors to the website and subscribers, I don't think the second option is likely.
>not every programmer is a Dr. Dobb's reader
Quite true. This is a problem inherent in all surveys. The survey size for these two questions were 1143 in 2010 and 500 in 2012, which statistically speaking would be fairly representative samples. The real rub is that programmers are not a homogeneous group, so the results will change a lot from one type of programming to another. For example, Dr. Dobb's does not cater much to embedded developers, consequently the effect that they would have on the charts is not captured.
If I assess the 2012 numbers based on what I know anecdotally, they seem acurrate insofar as capturing the broad trend towards polyglot programming. What was counterintuitive, at least to me, was how much the trend accelerated in the last two years.