Hikvision NVR. Lan connection v direct connection

OK so I got an NVR. The NVR itself was dead easy to set up and I've got three cameras also set up with it. All fine you might say but here's where I'm confused. The only way I could get the NVR to 'add' the cameras was if they remained connected to the router. The NVR saw them on the network and it was simples to add them. But forgive me if this is a really dumb question. I thought I was supposed to connect the cameras directly to the NVR? Whenever I do this they come up on my camera list...

Hikvision NVR. Lan connection v direct connection