I don't think it is body-shaming. The advert is body shaming. That is its very essence. It is what it is trying to do.
And it is an unrealistic body for a great deal women to achieve. Black women, older women, short women, women with thinner hair, disabled women etc etc.
I personally wouldn't have worded the petition like that though, I agree.
"So we shouldn't let a model show her body because most people don't look like that?" It isn't about not letting her show her body. It is about yet another advertising company buying into the same trope of what a woman should look like.