Straight from the copy on their website - "Zimaboard is a low cost single board server designed for makers and geeks like you." Or this one: "World’s First Hackable Single Board Server Starting at $119.9"
One could also argue this isn't a server because it isn't serving anything, it's just a powered down computer in a cardboard box in a warehouse, waiting for you to order it and tell it what to do, like any other computer (maybe you want it to serve stuff, maybe not).
The expected usage here is: This device goes under the desk / into some closet, runs headless, runs 24/7 and provides some services on the network. It's a server. That's how people use this word these days, RPi is a server device too. (See /r/selfhosted)
> The expected usage here is: This device goes under the desk / into some closet, runs headless, runs 24/7 and provides some services on the network.
The same is true of many configurations of home computers, yet the hardware isn't called* "server" hardware, and they aren't called* "servers" either, unless they're actually serving something. When you buy it at the store, it's just called a computer.
*: 'not called' as in, most people don't call it that, so descriptivist, and they shouldn't, so prescriptivist, too