Don’t know about Android but on iOS health information is something that an app can request on OS level.

There are valid uses for this, for example hearing level measurements from third party app can be added to Health app and then used for adjusting equalizer for AirPods via accessibility options. Or your menstrual cycle (although that probably won’t make your AirPods sound better) or many other data points. This is what Threads is trying to access.

It’s not about what you post but what data will Threads/Twitter/FB apps will trick you into sharing on system level (location etc).