I'm not making excuses for Samsung here but this IS the Verge we are talking about. Who knows what they did during testing. Maybe they can have the "how to build a custom PC" guy whip out his tweezers and take look at it. 😆
My best guess is that it’s a piece of debris, something harder than lint for sure. It’s possible that it’s something else, though, like the hinge itself on a defective unit pressing up on the screen.