The real story here, IMO is not that the internet creates more engaged citizens, but that being interested in something encourages civic engagement. [edit: not to say the internet doesn't increase engagement, it certainly does, but that's an obvious and uninteresting conclusion]

The idea seems to be to compare civic participation that's driven by [social v political v interest] factors and, from what I can tell, it appears that people who have hobbies and use the internet to build community around their interests are more likely to foster a stronger community in the physical world, whereas people who participate online out of political motivations tend to only increase political participation (e.g. campaign involvement.)

From the study: "Among all the predictors included, parental involvement, strength of ideology, college student status, and political interest were found to be strong and consistent predictors of increased politically driven online participation. Particularly strong, however, was interest-driven participation (B = .59, p < .001). The entry of interest-based participation in Model 2 accounted for an additional 19.1% (= 48.2%–29.1%) of explained variance in politically driven participation." [http://ypp.dmlcentral.net/sites/all/files/publications/Onlin...]