I made a meme about Bad Luck Brian mixing up euphemisms for masturbation in (what I thought were) funny ways about a week ago. I tried to get it flagged NSFW, but I couldn't.
So I don't really know the answer. I would have said "They flag it for the topic, not just the words," but if that's the case, I don't know why they missed mine. Good meme, by the way.