It is dense because it is meant to be. The skin is glutinous rice flour with sweet potato and oil, kneaded until it is chewy, about 90 calories for a 35g skin. The filling is the swing. Sweet mung bean paste at 25g is about 80 calories, which gives the 180 figure for a standard piece. The all green bean version with a thinner skin is about 141. The peanut version, with ground peanuts and sugar, is about 240 because peanuts are 60 percent fat.
One is a snack. Three is a meal. A box of 3 mixed ang ku kueh is about 550 calories, which is more than a plate of chicken rice, and the box gets finished in the car. The stalls sell them by the piece for about S$1.20, so buy the one you want and walk away.
The mini ones, about half the size, are around 90 calories each. The jumbo ones sold for prayers and birthdays are close to 300. Same kueh, three sizes, a big range. Look at the size before you decide it is a small snack.