Yes I know the difference. The state can force you to show your Nostr posts. They can do this literally with everything, including Bitcoin as well. In fact, most health checks were made with the regular CDC card, which is not signed. Adding things to Nostr doesn't change any of that. 

Tech is tech. The state can always fuck any stack. 

Also, the state already has access to your health data on today's system centralized systems. Adding Nostr, removes some of their existing knowledge of you because you can store it in your own relay, away from governments and b8g corporations.