I still have a FB account since it's the only contact I have these days with a lot of my highschool friends. I logged in earlier today and saw this "NASA is a hoax" garbage in my "suggested" feed.
There's nothing in my history to suggest I have any interest in conspiracy theories. My friends are probably right-leaning on average (I'm from a small town in the south - so it goes), but I clicked and none of them are in that group. So I'm sort of assuming this is promoted. Joy.
Facebook suggestions are based on nothing in my experience. It's all clickbait and bullshit. The worst part is that there's no way to turn this crap off.
I mean... I'm not seeing it anymore...
I suppose that advertisers pick some parameters like geography, age, groups before starting the campaign.
Easiest way to get rid of this spam when you're on Facebook mobile is go down to the bottom of the screen and flick up with your thumb. You should see your app launcher. Then flick up with your thumb on the window.