"To determine which posts are click-baiting, Facebook will take into account how long people spend reading an article away from Facebook. For example, if someone clicks an article and spends time reading it, the social network will deem the content valuable. But if users click a post and then return to Facebook, it suggests that they didn't find something they wanted, the company said."
But how does FB know I'm reading the article, not starting dinner or cruising Woot? Or that I didn't see the article, think "hmm, that's kinda long, let me save it for later."
I mean, I know Facebook's darn near omnipotent, but that seems a stretch!