They're talking about an e-ink being capable of that level of performance. You'd expect ghosting and noticable artifacts on the screen. E-ink is super slow.

They mean that the frame rate/responsiveness of that particular video shot is faked.

other sibling comments got it, the video/gif of the vertically orientation looks like it's photoshopped/video edited; faked.

there's no scroll lag between devices, nor image ghosting.

personally I think it's because it feels like that both the screen and the Iphone screens are edited on. Also, it feels like the finger flick scroll is too instant, I believe flick scrolling in Safari does not stop instantly but slowly slows down until it stops (unless it can be disabled). I could totally be wrong though.