I know it's against HN rules to ask if people have read the article, but you clearly didn't read the article.
The "non-sexual nudity" example is at the bottom of the article. It's a stylized cartoon drawing of a nude man and woman with arms around each others' waists viewed from the back as they walk along a path. There is a heart strategically placed around waist level so you can't even see their whole butts.
It's about the tamest artistic depiction of nudity you can imagine, certainly something that is totally fine anywhere else on Facebook. Very clear that this is a bullshit excuse being used by Meta.