520 calories for a full bowl with bread is honestly not bad for how satisfying this soup is. The mutton itself is doing the heavy lifting on protein, about 32g per bowl, which is solid. The fat comes mostly from two places: the mutton itself (bone-in cuts like ribs and shank have good marbling) and the rendered fat sitting in the broth. That broth is around 85 kcal for 300ml, which sounds innocent until you realize some stalls are ladling in way more oil than others. Fair warning: these are ballpark estimates. Hard nutrition data for Sup Kambing is thin, so treat this as a reasonable middle-ground figure rather than a lab result.
The biggest variable in the maths is what you eat it with. Skip the 2 slices of French bread (70g, 185 kcal) and your bowl drops from 520 to around 340 calories, which is genuinely low for how full you feel. Swap to roti canai instead and you're pushing 620 kcal. The other lever is the broth. Some stalls serve it cleaner, some are swimming in ghee. If you're watching intake, ask for less oil in the soup, it actually works at the good stalls. The mutton portion also varies a lot. The 200g bone-in weight here gives you roughly 110g of edible meat, so if your stall is more generous, add roughly 20 kcal per extra 10g of meat.