There are a number of obvious red flags in this story. There is no Sen. Cirenga, Italy doesn't have that many senators, and that amount of money would be 10 percent of the country's GDP. Nonetheless, it went viral during the election, was reposted credulously by several mainstream political organizations, and according to the authors, was "among the arguments used by protesters manifesting in several Italian cities" during the election.
The authors also divided users into groups who get their news primarily from from political organizing sites, those who mainly share content mainstream news outlets, and those who prefer "alternative" news sources: "pages which disseminate controversial information, most often lacking supporting evidence and sometimes contradictory of the official news."
They found that regular consumers of "alternative" news are far more likely to share false content. "We find that, out of the 1279 labeled users interacting with the troll memes, a dominant percentage (56 percent, as opposed to 26 percent and 18 percent for other groups) is constituted of users preeminently interacting with alternative information sources and thus more exposed to unsubstantiated claims."
I quibble a bit with the authors' use of the term "troll," which implies malicious intent on the part of the creator. The "Senator Cirenga" item included in the paper seems more like an Onion-style attempt at mocking the self-interest of politicians than a deliberate effort to misinform the public.
Clearly, people took this particularly story a bit too far, but this type of misunderstanding is less dangerous than the type of content spread by sites like superviral sites Natural News, which as Slate's Brian Palmer recently explained, "has an uncanny ability to move unsophisticated readers from harmless dietary balderdash to medical quackery to anti-government zealotry."