They don't show just one card the way I understand it. I thought I read where it said they fan the cards out to see them all, THEN they cut the deck and show the bottom card. If you have a photographic memory, knowing what the bottom card is you would then know the order of the whole deck wouldn't you? I don't have a photographic memory, so I don't know.
If they do fan the deck then yes it would be a memory thing. I would be screwed.