The author of this article and the Columbia Journalism Review should be ashamed of themselves. The article uses another study which as the article itself states

The author of this article and the Columbia Journalism Review should be ashamed of themselves. The article uses another study which as the article itself states didn't measure bias in news outlets but instead the self-reported political leanings of those who prefer the news outlets to classify news outlets as left or right leaning. Google may indeed mostly provide links to a few select major news outlets but the article is trying to go beyond this by suggesting a left or right slant to the outlets chosen and therefore to Google using data which doesn't support this.