Are you sure that ain't a GTX 650M? If so, It's a bargain, to get a MacBook Pro Retina performance for the price of a Mac Mini.
There's no way they'll fit regular GTX 650 on that small box.
The Haswell chip is also most likely a mobile chip.
I didn't really see the scale before, but the previous model is barely 10" long. I think you're right; there is just no way you could fit a desktop processor and graphics card in there, never mind all the other stuff. It explains the 70W TDP, too