I think they're referring to extreme calorie restriction.... unhealthy low calorie consumption & yea - that could be a disorder just the same as anorexia & bulimia.
I don't think what we do as 'calorie counters' or 'weight watchers' who keep track of our calories in order to meet a weight loss goal or maintain our weight at that goal would be the same thing. Most of us are eating a goal number of calories that is reasonable & healthy for us, not less.
(thanks for the link btw)
If you look at the Calorie Restriction Society's website, it doesn't seem unreasonable to me though... they mention eating less calories while maintaining proper nutrition. The average person DOES consume too many calories - and could benefit from what they suggest IMO.