The Obama campaign got a lot of mileage in 2012 over a comment Mitt Romney made in private which was overheard and, if I remember correctly, recorded by a Democrat who happened to be within earshot.
Of course Sterling is a Democrat and a billionaire, but the intended message was that Fox and conservatives generally are racists.
Of course FNC is not really conservative, but the fact that they include some conservatives in their lineup means that the mainstream media and the Democratic Party regard them as conservative.