Hard to remember almost 5 years after that post but I think they said it made them bloated and gave them puffy nipples. The latter concerned them more since it affects the appearance before and during competition but I think the bloat is the more telling sign as it suggests it either stimulated endotoxin or gets into the blood not full digested and triggering an immune reaction there.
That's strange, breast milk supposedly contains a lot of hydrolyzed protein. Hydrolyzed protein is used in baby formula as well, and is generally advertised as being hypoallergenic, easier to digest and assimilate due to being "predigested".
A lot of protein products contain 150mg+ soy lecithin per scoop which could also give an estrogenic effect. Plus a lot of these products have flavors, gums like xanthan gum, possibly carrageenan, guar gum, and sweeteners like sucralose, stevia, acefulsame potassium.