Sorry, I re-read my post. I meant the elements are *hashed. Hashing means passing something through a one way function like a message digest. A hash acts as a statistic or code that can be generated given a piece of data, but that cannot be used to figure out the original message. It's similar to encrypting, except that when you encrypt something, you also have a way to decrypt it. In this case, we see if a particular nevent matches by just hashing it and checking to see if the result is the same as what we recorded for an undesirable nevent. Sorry for the typo!
Discussion
Hash databases would definitely be better, and might help the maintainer avoid liability, but public hash databases (in particular for fuzzy hashes) can make it possible for attackers to reverse-engineer the hashing algorithm to craft payloads that avoid matching.
nostr:npub1g53mukxnjkcmr94fhryzkqutdz2ukq4ks0gvy5af25rgmwsl4ngq43drvk doesn't care. He doesn't feel responsible for child pornography on Nostr one way or another. We aren't necessarily talking about a sophisticated CSAM detection algorithm or fuzzy hashes to prevent someone from uploading previously identified media. He is talking about blocking individual nevents and only those nevents that are reported to him by Cloudflare.
Personally, I think fuzzy hashes and content detection are fascinating and important topics just for reverse image search and detecting when someone reposts certain content.
However personally I don't give a shit whether someone pirates CP. If someone doesn't realize how bad pirating is then that's their problem. I believe that when a child is raped, trying to prevent anyone from seeing it and trying to keep any evidence of what happened off of the clearnet is the most asinine, shortsighted, and selfish possible thing to focus on.