It really doesn't. Consoles are a completely closed off system, to the point where modifying it can get you banned from online services. The Deck is the complete opposite to that, with Valve even explicitly encouraging you to tinker with it. It always has been advertised as being a full PC, because you can do all the things you can do on a PC. You can literally go into desktop mode and have your regular KDE Plasma screen.
By your definition every gaming PC would count as being a console. That's just nonsense.