I think their point is that there are women/girls with eating disorders (and those recovering from them) whose behavior is triggered by that type of language. They hear someone rationalizing a snack (or talking about counting calories, etc) in a perfectly healthy way and it sparks disordered thinking/habits. People with eating disorders often don't have a concept of moderation and a varied diet. Do I agree with advertisers altering commercials to tiptoe around mental illnesses? No. I think these girls (and boys, in some cases) have very altered perceptions that are not going to be cured by the absence of yogurt commercials. If they don't find justification for their behavior on TV, they will find it elsewhere. The commercial wasn't removed because they think it makes women feel bad about wanting cheesecake; rather, it was brought to their attention that it raises ED issues and they wanted to cover their butts. Again, I don't agree with that but it's their call. They are generating more press now than they did with the initial commercial.
I think when the article asks "Can an advertisement trigger an eating disorder?", I think they are a bit off the mark. They should be asking "Can the advertisement trigger disordered behavior?" "Normal" girls/women (for lack of a better term) are not going to start puking up their breakfast because the weirdo in the commercial chose yogurt.
And for the record, I would never DREAM of choosing yogurt over cake or pie. If anything they should've stopped running the commercial because it was stupid.
ETA: If you're ever interested in the subject, Portia de Rossi's memoir "Unbearable Lightness" is a very interesting look into the mind of someone with an eating disorder.