Each side of the political spectrum has a spectrum of biased news. For example, Huffington Post and The Young Turks are liberal news sources which are very partisan. The Economist is a fiscally conservative magazine which is less partisan, Uncommon Knowledge is an interview show with a conservative viewpoint, but also an educated and intellectual viewpoint.

If you're a liberal minded person, your exposure to conservative sources of news is likely excerpts of their most grievous offenses. Hence, the liberal bias suggests that conservatives get all their news from Tucker Carlson making funny faces at people, or Alex Jones identifying gay amphibians. The result is the belief that liberals are reasonable intellectuals and conservatives stupid fools.