The Census data I cited is net interstate migration. Review the last page of the PDF I linked. The title of Appendix Table A-1 from which I quoted is "Domestic Inmigration, Outmigration, and Net Migration: 1995 to 2000." It's simply the first link I found and as such it's not the same time period as the WSJ article's subject. But I figured it was a data point that at least superficially corroborated their admittedly-unknown underlying data. By that, I mean that it provided sufficient credibility to their discussion and confirmed it was a matter of migration and not population. From there, I considered their conclusions at least plausible.
You say, "There is always a natural tendency for some people to go from populated areas to less populated areas."
According to the 2007 data represented at the URL below (which I have not traced to its source, but I wouldn't be surprised if it too leverages Census data in some fashion), there does not seem to be much correlation between population and migration.
http://www.pewsocialtrends.org/2008/12/17/u-s-migration-flow... (Warning: Flash required)
The greatest net outmigration is Alaska with a net migration of -60,000 and a population of 683,000. Meanwhile, many states with populations between 5M and 20M had net inmigration.
While it seems plausible that there could be a natural tendency to migrate from high population to low population; the reverse seems just as plausible. California had a relatively high population when it had net positive migration. Texas currently has a high population and a net positive migration.
It seems clear to me that more significant variables are at play than just a desire to switch density levels.
Are those causes dysfunctions? Maybe; I suppose it depends on what you consider dysfunctional. Another poster in this thread pointed out that California's Proposition 13 is a distorting influence. Is it dysfunctional? If you own property, you probably think Proposition 13 is a good thing. If you do not, you probably disagree.