They're rigged to follow the camera, so they look normal from that perspective, but they look like this from a different angle (in the viewport).
It's like using cardboard cutout people for crowds in live-action movies (which they do, sometimes).
Anyway, they don't take as long to render as modeled characters.
I understand this technique is used a lot in games.
I'm in the process of building up a crowd of on-lookers for this shot. Although there will be some duplicates in shots like this, I'm still working on differentiating panels by changing the billboard images.
