They don't. They're just sending these to all communities of a certain size that switched to nsfw recently. Most of them are in fact allowing nsfw content (like profanity) but it doesn't matter. The ones that tried allowing REALLY nsfw content got punished for that too.
How do they assess if its an incorrect label? I think the horde of goblin porn should be classed as pretty NSFW?
They don't. They're just sending these to all communities of a certain size that switched to nsfw recently. Most of them are in fact allowing nsfw content (like profanity) but it doesn't matter. The ones that tried allowing REALLY nsfw content got punished for that too.