Those steam boxes are PCs. They work just the same as normal PCs on a hardware and software level, contrary to game consoles which are closed and more customized. You can't go and install the plethora of software available to PCs on a PS4 or XBox One. You can't install Photoshop or Office on a PS4 or XBox One. But you will be able to do so on a Steam Box. You'll even have the possibility of changing the OS entirely if you so wish. Something you can't do on a PS4 and XBox One.
Someone mentioned that the XBox One is a PC because it runs a version of Windows 10. But that version is a closed and customized one, tailored to handle a very specific set of features, and it doesn't allow any of what I mentioned earlier for the PCs (installing third parties software of all kinds). Consoles and PCs are getting more and more alike, but they're still not the same thing at the end of the day. One is an open platform, the other is closed and dedicated.
So no, Steam Boxes aren't game consoles. They're glorified gaming PCs.
