* The fact that FOX news, being a major news network that airs on a media device presumably available to millions of people across the country doesn't consider itself to be "mainstream" media -- how is it not "mainstream"? It's not as if FOX news is some underground news wire available exclusively to a select group of individuals. It's as mainstream as MSNBC and CNN, just with a right-wing viewpoint.
** Probably an example of InsistentTerminology. "Mainstream media" is often used as a derogatory term that FOX News might want to avoid, see StrawmanNewsMedia for details; "mainstream media" is sometimes skewed to mean "with a Liberal/Democratic slant."