What jurisdiction is the forum under and under what circumstances could you be forced into providing information relating to a forum user? Like if you were living in the US and then a subpoena came by forcing you to provide the information, I'm not sure there is much way to avoid it.
I believe the forum owners and server(s) are located in the United States, and cannot avoid being subject to US jurisdiction.
If theymos were to travel internationally, he would be subject to that country's laws. I don't see Europe (or most other countries) subjecting theymos to their data laws if he were to go on vacation for a few weeks.
If the forum has any employees (or moderator 'volenteers') who live overseas, their governments could arrest the moderator and hold them hostage until theymos complies with their requests. I would consider this unlikely in western countries, however I cannot rule this out with regards to China. If the moderator of the Chinese local sub (or any other mod) is based in China, theymos should consider terminating the moderator relationship, or at least have a conversation with the moderator to make sure they are aware the forum has no intention of complying with requests for information on political enemies of the CCP.
The moderators should also be made aware of the above policy, and the risks associated with traveling to Hong Kong should be highlighted to the forum's moderators.The CCP has a history of "hostage diplomacy" as they arrested Canidian businessmen (on bogus charges) after Canada arrested a Huawei employee at the request of the US government.
Since this forum uses CloudFlare to prevent DDoS, i think OP's question also applies to CloudFlare as well.
CF appears to do business in China, and this should answer your question. They may not have collected information on specific users, but may start if the CCP requests they do so.
I believe google cloud services has a DDoS protection product, and google is unable to do business in China (and importantly, are not responding to requests for information from the HK government).
Someone who has criticized the CCP, or has worked towards bringing Democracy in Hong Kong may be subject to life in prison, or possible torture. This fact should be carefully considered before handing information over to the Hong Kong or Chinese government willingly, even if they are possibly guilty of other crimes.