Is the user expected to know about OS packages on it. Are they installing/updating software components by hand, so they know the OS version which runs in the box even, are they calling it a "server"? If the answer is yes, it not "embedded".
If they interact with the device as with an appliance (a dvd player, microwave, car infotainment center, some radio base station and so on), then it is embedded. It can still be an 8 core Xeon monster, but because of how it is serviced and used it, I think of it as embedded.