Paru Goreng is beef lung, deep-fried with a spice marinade of turmeric, coriander, garlic and shallots. If you have not had it before, think of it as the chewy, crispy offal piece sitting in the tray next to the rendang at nasi campur. The texture is very different from muscle meat, slightly spongy inside and crunchy on the outside, and it soaks up oil like a sponge in the fryer. At 390 calories for a small 80g serving, it is one of the heavier lauk choices per gram, driven almost entirely by that absorbed frying oil (145 calories worth) rather than the lung itself (210 calories). The protein return is genuinely solid at 32g though, so if you are tracking macros it is not a terrible trade, just be honest about the portion.
The maths here are almost entirely about the frying. That 16g of absorbed oil is the swing factor. At a nasi campur stall you have zero control over how hot the oil is or how long the pieces sit in it, and cooler oil means even more absorption. If you take one piece instead of three you are looking at roughly 130 calories, which is a lot more manageable. Pairing it with lower-calorie lauk like steamed veg or a broth-based dish helps balance the plate. Swapping to ayam goreng gives you a similar fried-protein hit but around 280 calories for a comparable serving, so that is one way to shave 100 calories off your plate without feeling like you are eating a salad.