Hmmmm... I don't think this is a lighting issue. That dress looks very sheer. It may have been less obvious in dimmer light, but I suspect if you put your hand up to that material, you'd have seen right through it even indoors. It's awfully hard to think this was inadvertent....
Most likely you are right, that sheer and teasing was what she was going for, but didn't take into account how much would show under lights and camera flashes.
I don't think she planned to show quite this much.