We've nee collecting top rated news from Yahoo News, NYT, Washington Post, etc for the last 3 years. Almost all major sources have sections "Most viewed", "most read", "most email" etc. So as we have been collecting the top ranked news we also kept track of topics that have been top ranked at multiple sources. For instance, if a news article on Iran's riot gets to the top ranked in both NYT and Yahoo News it gets more points in our training set.
As far as your other point, Misleading is really a less legally loaded word than "deceptive". You are right, it's not very clear why the articles are misleading but the bottom line is that the language used in the article has high "deception markers" that other articles from the day. So when you sort by Misleading, it's not really that the article is beyond a doubt deceptive, it's just the ones with higher rate of deception markers (i.e. content and structural indicators associated with deception). The science behind is pretty solid and comes from forensic psychiatry - i.e. interviews/interrogations with criminals and analyzing their statements for deception hints. So for alack of a better term Euraeka essentially implements a linguistic polygraph.
Thanks for the other comments, we'll work on fixing the issues.