Condensed milk is 320 calories per 100g, so the number is just how much the seller pours. A careful 30g pour (2 tablespoons) is 95 calories, which is the Long Chau figure. The 40g that most street quan use, because customers complain if it is not sweet, is 130. A big 50g pour at a quan that serves it in a tall glass with the spoon standing up is 160. The 40ml of phin coffee adds 2 and the ice adds nothing.
The habit is the issue, not the glass. One ca phe sua da a day at 130 is 910 calories a week, 47,000 a year, which is about 6kg of body fat if nothing else changes. Two a day, the normal Saigon office pattern, is 12kg. It is the single most common reason a Vietnamese person's diet does not add up on paper: the food is fine and the coffee is 260 a day.
The alternatives are close cousins. Bac xiu, mostly milk with a little coffee, is about 105 in Long Chau's list but 180 to 220 at chain cafes that use fresh milk and condensed milk together. Ca phe sua tuoi (fresh milk) is 135 in the same list. Ca phe den da with no sugar is 5. Ca phe den with the standard spoon of sugar is 40. The gap between den and sua is 125 calories and about 22g of sugar.