If $5k is worth the risk of losing their job, they're not making much money at Facebook, nor think there's potential for much growth in the role. Losing that job isn't going to be a big deal for them, and the article doesn't suggest any legal action may be taken against them.
It's another argument, but I think it's on Facebook entirely that they don't pay their employees enough, keep them happy enough, to prevent this sort of thing from happening. When you leave content moderation to your lowest paid employees, you are only encouraging people to figure out how to game the system for more.
I think you're making the mistake of assuming people always act rationally. There are countless anecdotes of well paid, ostensibly happily employed people losing their job over juiced expense reports or similar small (in dollar terms) schemes.
It's another argument, but I think it's on Facebook entirely that they don't pay their employees enough, keep them happy enough, to prevent this sort of thing from happening. When you leave content moderation to your lowest paid employees, you are only encouraging people to figure out how to game the system for more.