She has her arms raised and kinda leaning back, so she's showing a lil bit of her belly and the rib cage, so it's the angle not the drawing, but yeah those are her ribs, why so bad? She's a cute slim drunk girl xD
It's a bad use of perspective, that's what it is. The image is done entirely too flat (no pun intended) to simulate depth, which is what that kind of perspective trick is for.