The number surprises people because there is nothing creamy or deep fried on the plate. But the wok needs a lot of oil to keep 400g of flat rice noodles from tearing, around 30g per plate, and rice noodles themselves are dense. CFS measured 140g of carbohydrate in one plate, which is the same as three and a half bowls of white rice. The beef is only about 100g, so protein is a modest 26g for nearly 1,000 calories.
Among Hong Kong fried noodle dishes this is actually mid table. Singapore fried vermicelli is 1,100. Fried noodles with black bean spare ribs is 1,500. Fried instant noodles with pork chop is 1,200. Beef ho fun at 970 is the one everyone names as the villain because it is the most ordered, and a dietitian in the HKET ranking pointed out it does not even make the top three. That is not a reason to order it twice a week, just context.
Portion size at a dai pai dong is the real issue. The 650g CFS plate is a standard single order, but the plates in Sham Shui Po and Mong Kok that come with a mound of noodles hanging off the edge are closer to 900g and 1,300 calories. Sodium is 2,300mg a plate from the soy sauce alone. If you split a plate between two people and add a plate of greens, each person gets a 500 calorie meal, which is reasonable.