I’m also confused because based on that screenshot, the page has HTTPS, which would mean either the block would be client-side, or the entire domain is blocked.
If it's a Chinese run spider that flags websites that contain banned terms, does this mean that we can effectively block certain websites from China as a form of denial attack?
There are many sites which allow user submissions without a strong administrative overview. E.g. Could Booking.com be blocked to the Chinese audience by a listing including certain keywords on their page or in imagery.
Yes? That's basically why a bunch of western social media sites are banned in china, because people post subversive content there and the site's administration refuses the government's request to take it down. If you tried it on booking.com or whatever, it won't work, both because your comments will be taken down by site administration for being off topic, but also because the site is big enough that they won't take automated actions (hopefully). At best you can take down small to medium sites that don't have active moderation teams. Moreover, this isn't an attack that's limited to china, it can be used against any sort of content blocking system. Sites have been blocked from google browsers (via google safe browsing) due to malicious UGC, and you can even take down the whole site if you email the abuse department of their hosting provider.
The comparison was with how both the chinese censorship system and other blocking systems can be susceptible to the same attack (ie. people posting UGC to get a site banned). At no point did I imply that they were comparable in any other way.
I believe this is known. I have a file saved somewhere with a list of terms that allegedly trigger Chinese blocking.
I won't post it here :) It's pretty useless, in a practical sense. If I say anything the Chinese government wants to block, I'd rather their citizens see it.