You likely hit on the difference, here:

"mirroring each other on the network"

The NAS can be Attached to a computer, as I pointed out, and that makes it Managed. Or, attached to the Router, which makes it Common, not Managed.

You can see the difference in the installation types if you go to the image I linked.

It's like this:

Three of us in an office share a company vehicle. There is one set of keys at the front desk. When you go to get them, you find out I already have them and have the car.

Or,

We each have our own set of keys. There is no way for you to know if anyone else already took the car.