The rice is the whole story. A cup of cooked white rice is 200g and about 260 calories before anything touches it. Sinangag adds roughly 1 tablespoon of oil per cup, which is another 120 calories in the pan, but only part of that sticks to the rice. Kawaling Pinoy's recipe card puts it at 247 calories per cup with a quarter cup of oil across 4 cups of rice. A carinderia uses more oil than a home cook, so 300 is the fair number.
Where people go wrong is the second cup. Silog plates come with 1 cup, and an extra cup of sinangag is 20 to 25 pesos. That second scoop turns a 650 calorie tapsilog into a 950 calorie tapsilog, and the tapa did not change at all. The garlic and salt make it very easy to keep eating, which is the point of the dish and the problem with it.
The oil varies a lot by cook. Some carinderias fry the garlic in lard or in the fat left over from frying longganisa, which makes the rice taste better and pushes a cup closer to 350 calories. If the rice looks shiny and leaves a film on the plate, count it as 350, not 300.