I think its the notion that its a game first device, that also happens to do pc stuff. Like you mention, the lines get blurry as theres always weird exceptions (e.g. xbox having dev mode allowing for unique softeare to be ran, also can technically run microsoft cloud edition if you wanted something computer like, or like the PS3 being able to run "OtherOS" before sony backtracked on allowing PS3 users to run Linux on the device. Would fall under the same kinda distinction that seperates a laptop and a "gaming laptop" drspite it functionally being the same.

The only differemce is valve tailored SteamOS in a way thats console like, despite its linux internals, almost in the same way that Xbox's os is a severely stripped down version of Windows but is still windows nonetheless