Considering it's not taking things from both, it would probably be optimal to put stuff from Anidex to the side, take things from Nyaa if they appear there, and leave the rest (that wasn't already filtered out) to human review.

That would solve the problem for Anidex while, even if late, keeping Releases that are only there.
But obviously its on Admin-san to decide if that work for him and/or whoever he trust is worth it.

I think what the Admin has done for this website is already enough. Such features will just add more things for admin to deal with.

I don't have an account here, but could one way to possibly reduce / prevent this is to have registered people have the ability to "report" submissions, and when a certain threshold is reached, the link is automatically hidden from public view until manual approval? It would probably be abused though, but hopefully less so especially if users are registered...

Thanks.
There are filters in place to try to exclude these posts, but they didn't catch it this time. I've added more filters, but how effective they are remains to be seen.
It's unfortunate, but automated filters are rarely 100% effective.

I think people are mis-attributing the problem to Anidex. I very much dislike their lack of moderation, but Nyaa has had CSAM posted several times, even after registrations were closed, so it's not a problem unique to Anidex.
Having said that, I'm very much in favour of dropping Anidex if a better alternative exists*.

It may surprise some, but there actually are numerous filters in place, which has had varying degrees of success in the past. Unfortunately, the people posting this stuff are often trying to evade filters to some degree (using misspelt words, posting many variations to see what passes through etc), which is easy for a human to identify, but not so much for a bot.
Nonetheless, I've added more guards in place to hopefully deal with it better next time. Unfortunately, nothing is 100% effective, and as much as I detest it, it's a risk that running AT bears.

Highly appreciate the suggestions though!

* I'm actually a bit on the fence with dropping Anidex, even without an alternative. This isn't because of the recent incident, but more of it's managed in general.

CSAM distribution is a serious offence. any reports regarding this matter will be dealt asap. So no surprise there.

no Anidex no worry but no AnimeTosho big worry

To me the weird thing was the registrar going along with this.  If he scrolled back a page he would see this was a blob of gunk with nothing before it.  I don't think anyone would have expected such a reaction.

Makes me wonder if maybe it was deliberate - someone gets a third party to flood AniDex with CSAM such that AniDex categorizes it as English-translated anime (so AnimeTosho picks it up), then they immediately contact AnimeTosho's registrar in order to report it and get the site taken down.

Stranger things have happened, after all.

Oh yes I see the post now, yesterday 11:08. Well that's kind of weird the registrar pulled the plug not even 24h of it occurring, and why they were watching the site so quickly -- or how quickly someone reported it. Curious as to why AniDex wasn't taken down, probably different registrars and no one watching. I agree with removing AniDex.

since admin is willing to deal with it, I'm not going to worry about it.

yes, admin confirmed that earlier in feedback

Was it confirmed that the Anidex event was what caused the site to go down? If it is then obviously I'd agree.