To answer your question, straight sugar is high in calories but low in fat. Its high in simple carbohydrates.
That said, I'm not sure the advice you read was so great. It likely comes from the outdated belief that dietary fat/cholesterol equals fat/cholesterol in your body. Eat too much of any of the 3 macronutrient categories (protein/fat/carbohydrate) and you will get fat. Eating huge amounts of simple carbohydrates and the associated sustained high blood glucose levels over a long period of time can put a strain on your pancreas and in some cases lead to diabetes, varying levels of insulin resistance, and arterial plaque.
If you want to put on weight, you have to decide what kind of weight you want to put on. If you want to put on fat, the best way to do that is just to eat lots of food with little or no exercise. If you have a normal digestive system then there is always a point at which your body fails to burn all the calories you consume, and you put on fat. If you have a faster metabolism than average, this will be more food than others eat.
If you want to put on muscle, then you have to train hard in the gym whilst eating lots of quality food.
I hope that answers your question.