This seems right to me. Philosophers have long objected to assumption that what is natural is what is good. See for example, this video explaining Moore's 'naturalistic fallacy' and this more focused version.) Many bad things are apparently 'natural': disease, death, violence and anger. Many good things are 'unnatural': medicine, the internet, universities,etc. Moreover, when we consider that humans are part of nature and naturally technological, the very definition of natural seems questionable.
However, I can understand the motivation for stressing the naturalness of breastfeeding. First, breasts have lots of amazing features (for example, the way in which they adjust the content of the milk to fit the baby's needs) and it seems likely that this is connected to the way in which breastfeeding has evolved through the marvellous process of natural selection.
Second, there is a significant need to normalise breastfeeding, so that breastfeeding mothers can get on with their days and go out and about without being forced to cower in toilets or lurk under a sheet every time their infant needs a drink . When women who breastfeed in public are told that they are 'disgusting' or 'attention seeking' then we might well want to respond by pointing out that they are doing the most natural thing in the world.
Again, the difficulty is how to encourage and support breastfeeding without either stigmatising those who make other feeding decisions or having other unintended consequences.