I think cards actually tend to get reported for being posted in irrelevant communities. For example, if the card was like this one, it doesn't really belong in the Learn Japanese community, if that helps
I think what @OtakuDemon10 and @Thatperson512 said makes sense. It's important to think about who you're sharing with when you publish cards. A lot of communities (I know anime is one of them) are trying to be kid friendly
they also want buffer images warning mature content. you probably just posted something some mom saw on her 12yr Olds feed and she thought it was in bad taste. just watch what you post, follow the rules they have and it'll be okay!