What he's alluding to is that currently conservative voices seem utterly incapable of just not lying. Fox has progressed from a bias, to misinformation, to now just straight up disinformation.
When that is the other "side", then honesty will seem biased. The middle is would be something like lying 25% of the time.
"Reality has a well known liberal bias." — Stephen Colbert, 2006 White House Correspondents' Dinner, https://www.youtube.com/watch?v=IJ-a2KeyCAY&t=4m11s