If you enable the “remote access” in Plex you are essentially port forwarding you server to the internet using UPnP (by default. You can also port forward manually if you’d like).

It’s indeed a point to point connection but a point to point connection the same way your connection to normal websites are point to point.

If you knew the public IP of anyone that’s using Plex you can likely go to [IP]:[Random PORT] and access their server. You still need to login though.

Source: My own tests and …plex.tv/…/200931138-troubleshooting-remote-acces…