It was Stephen Colbert, back in 2006 during a White House Correspondents' Dinner, which of course was during the Bush administration. The exact line is "Reality has a well-known liberal bias."
And I think it's true, only because of how much bullshit right-wing journalism creates. Sure, all journalists have bias. Editors will choose which stories matter, which facts get included, and what context gets emphasized. But right-wing news outlets come up with outright fabrications based on nothing.
Haitian immigrants eating pets. Dominion voting machines switching votes in 2020. Tons of lies of what really happened on Jan 6. Schools putting litter boxes for students who "identify as cats". Basically anything spouted by Alex Jones.
And that's just the more recent stuff. Go back to 2016 and the bullshit was off the charts. Yelling about a child sex trafficking ring being run from the basement of a pizza place that didn't even have a basement.
That doesn't even get into issues like human-caused climate change, which the right continues to deny.
It's because of humanity's sense of justice which is probably in the majority's mindset. Can't back it up with data or research but I think the majority of any population would vote for measures like e.g. reducing the wealth gap. Hence "reality has a left wing bias".
No, reality has multiple sides. Outside of a few right wing channels and blogs, most reporters and comedians are leftists - which isn’t representative of the total population whatsoever.
Stephen Colbert. Finding the clip is left as an exercise for the reader.