You're right, the torso is bent to the left (his right), that's why we can see the pinch on the left side of belly and a stretch on the right side of the belly. And actually, if you look closer there's a protrusion on his right tip of the rib cage. You see, the reason you can't see the protrusion at first glance is because Yoni is particularly huge and muscular man. If you've seen him posing in live, you'll see how big he is. And it's also the exact reason why you didn't see a curve on the left (his right) belly. I've attached the skeletal and muscular sketch over. As you can see, his external oblique is so thick that it makes itself look straight from this particular angle. Should he's smaller or thinner (image 3), we will definitely see a curve right there.

Hi Anubhav, I don't know if you can tell from my attached scribble. First of all this is an overhead shot (also with some foreshortening as you can see from Yoni's left leg), so you see both the upper part of the ribcage and the pelvis (although this one more foreshortened). The ribcage is slightly bent to the right because the arm is stretched forward and the hand rests on the knee, for the same reason the ribcage is slightly rotated in relation to the pelvis.

Hey Anubhav, Remember, the shoulder girdle is independent of the torso. It floats on top and can move up and down and forward without affecting the torso. You should try it out yourself, and feel it in your own body. What's happening here is that the torso is pretty straight, but the shoulders are tilted forward and down. Hope this helps :)

The rib cage is mostly straight in this one. Most of the twisting (therefore pinching) appearance is coming from his left arm being brought slightly to his back (posteriorly rotated) and his right arm being brought forward (anteriorly rotated). I think your issue with understanding the direction of the rib cage comes from the fact that the rib cage’s opening for the head is not parallel with the rhythm of the whole cage. The whole anatomical rib cage’s rhythm itself is kind of “laying back”, and the torso in total is more vertical. The opening of the head is more forward (3). I’ve drawn (or how I understand / would think if I were to do a study) this pose’s rib cage (1), the angle of the torso as a box (2), and as the bean (4). As you can see, the rib cage does not seem to follow the rhythm of the torso. This is probably where your confusion comes from.