Actually when I read the title, I assumed it implied the causality going the way that makes sense (e.g. "FB addiction linked to need for social acceptance" = "FB addiction caused by need for social acceptance").

Upon further reflection, for me, I don't think the verb "linked to" implies any particular direction of causality. I would find it reasonable to word a headline as either "diabetes linked to twizzlers" or "twizzlers linked to diabetes", even though the causality clearly can only go in one direction.