Actually, it is a nintendo authentic. i dont remember where i read this but a couple weeks back back nintendo released about 250 models of the "demo" versions across the USA to be used at places like gamestop and babbages to inform more of the public that its coming out soon, and so people could get the feel of it.
thats why you didnt get a transfer cable. you are in a way kind of lucky, and in a way you should feel ashamed because somehow you managed to mooch a demo off gamestop, :D Lucky!