The logic behind any weight gain/loss program is that you need to look at the amount amount of calories in vs the number of calories used. Telling somebody to follow a 2000 calories diet is based on pure guest/estimate of the person metabolism and lifestyle

eat less : not necessarily

One thing you have to note is that calories are a measure of energy and not a measure of quantity so saying eating less does not have anything to do with weight gain/loss. It all depends on the amount of calories the type of food you are eating will provide you ... a mars bar will give you pretty much the same amount of calories as eating 3-5 chicken breast ... so the quantity of food is not related at all

Eat better : Agreed

Calories comes from 3 differents sources (protein, carbohydrates and fat) ... it is very true that choosing the sources of your calories will have an impact on your weight

move more : not necessarily

Like i said it is all based on the amount of calories that you give to your body vs the calories that are used. Having a goal of losing weight implies that you will need to either give less calories to your body then he needs or burn more calories that you are actually giving him
Someone who dosent want to move can still lose weight but the input will have to be changed