Public IP working for Hikconnect DDNS but not manually?

Hello!

So I'm a bit lost here, I have a HikVision NVR, connected to the internet, and added to my HikConnect online account. On my device details, it shows the public IP of my NVR network, and the port used.

Trying to connect manually to this public IP address and adding the port of the NVR however does not work (I am not connecting from inside of the network).

Moreover, the ports that Hikconnect is using seem closed in openportchecker, however I can normally access my NVR remotely via Hik's app.

Finally, Hikconnect seems to work without even having to open the ports manually via the router.

I am quite lost here, anyone can explain what is currently happening? Thank you very much.