That's just saying that highly-trafficked, highly-edited articles are going to be less biased than articles with fewer contributors or sources. That... just makes sense, to me; the more visible or relevant an article, the more people (and potentially experts) will weigh in, and the more crowd consensus will drive out the more blatant biases.

It also mentions there a bias in both directions, depending on the topic. Plus, it only considers US viewpoints/political alignments, and not Canadian, British, Australian, or other countries.