The broth is water, tamarind, tomato and fish sauce, so a cup of it is about 15 calories before the pork goes in. That is why sinigang is one of the better carinderia soups if you are counting. The number only moves when the cook uses liempo instead of ribs. Pork belly is around 350 calories per 100g cooked, so a bowl loaded with three thick belly slices can hit 450 to 500 while a bowl with two rib pieces stays near 300.
The rice is where sinigang gets expensive. Nobody eats it without at least 1 cup of rice (260 calories), and sinigang broth on rice is the specific reason people go back for a second cup. A standard lunch of one bowl and two cups of rice is 840 calories. The soup did not do that, the refill did.
The oil floating on top is real. Belly fat renders into the broth during the 45 minutes of simmering and forms a layer of about 15 to 20g in a family pot, which is 130 to 180 calories spread across the servings. Some carinderias skim it, most do not. Ask for a bowl from the bottom of the pot with more vegetables and less of the top layer.