Its very simple^^ I did rotate the back card in Aseprite, which tilts the artwork but keeps it all on the pixel grid. I then fixed the skewed pixels so it doesn't look bad. It only works because most of the card is hidden by the one in front, because this is how they look without:

I think it's because it's such a slight tilt that my brain sort of smoothes out the pixels breaking up the line and treats it as a whole if I don't look at those pixels directly. Whereas on a more angled line without AA there would be too many edges too frequently for my brain to ignore at a glance