Bitcointalk.org is not subject to Hong Kong / China jurisdiction, so would not be required to produce data in any case. If some police wants data without a subpoena, they have to convince me that a serious non-victimless crime (eg. scamming) probably occurred. I certainly wouldn't help them if it looks like they're going after political enemies.
Most ideally, requests for information from China/Hong Kong would be ignored, but I suppose the procedure you describe is sufficiently close.
But if you're in Hong Kong or other dangerous places and you're worried about this, then you shouldn't trust
anyone to protect you: not me, not anyone. Use Tor everywhere, and on bitcointalk.org practice the
privacy-enhancing measures mentioned on the privacy page.
My understanding is the national security law bans calling for democracy in Hong Kong
worldwide. This means being outside of Hong Kong will not protect you if you later travel to Hong Kong. I understand someone calling for democracy in Hong Kong while in the United States, Europe, Africa, or anywhere else would be subject to arrest if they later traveled to Hong Kong.