There is a great difference between saying something is biological in origin and something that has biological influences or pre-disposing factors. If eating disorders were biological in origin, then the most effective treatment would not be psychological counseling, it would be medication, nutritional or lifestyle change. The web site referenced has great deal of emphasis on "body image". That is a self perception issue not a "biological issue". Having a driven temperment with the tendency to become obsessive/compulsive can be biological and thus pre-dispose someone to eating disorders and addictions.
Why their is such a link to female distance runners and eating disorders is probably due to the driven/obsessive nature of many runners to begin with. I would venture to say the reason the African runners don't appear to have as many problems is that "Body Image" is not near as strong of a cultural factor, at least not the image of being thin.
It is a terrible epedemic in which the cure can only be found "close to home". Please support these girls and those who are helping them. Encourage all of the "girl runners" you know to "fuel" their bodies and not fall into the trap that less body fat is better. We only get one chance at life!