Because it raised a complaint that had nothing to do with the article. That's an article describing the results from a study on self-reported happiness level through people's lives from 1.3 million sample respondents. The question about "misfortune" is a non sequitur -- out of the scope of the study, and irrelevant to it. Those 1.3 million random samples will still have the same distribution of misfortunes as the general population in their countries.
Second, because it didn't seem to differentiate between a journalist reporting on the results of a survey, and those that did the survey.
Third, because I don't find the article poorly written, and I don't particularly care whether someone "flagged" it or not -- reminded me of those who bring up "cancelling their subscription" in their letters to the editor.