Apparently they've made a change where posts from groups you're not a member of can appear in your feed (being slowly rolled out). Perhaps they figured they can't get away with that if the news headlines said they were spreading conspiracy nonsense to people unwittingly.
I've been noticing this on my feed! I keep reading posts thinking they're from a group I'm in then realising it's not. Fortunately it's a group that's pretty closely related to other groups I am in, but I can see this becoming an issue down the line (like most FB changes seem to end up), with them pushing groups on you that are either completely unrelated or funded by dodgy bastards peddling nonsense.