Accessing VM through browser outside local network

[oRBIT]

Assume I startup my VM in VMM in DSM and access the VM from outside my network (using the browser-solution, VNC isn't it?) and perhaps starts a webbrowser inside it. Assume someone is monitoring network traffic on the same network I access the VM.. What is actually visible? Only traffic from/to my NAS and nothing else? Hope you guys understand what I mean..
Just curious how it all works..