I've always believed reports of threats of termination disseminated through Facebook are obviously the best form of confirmation that you've got the real deal when an image of a new car leaks way early. Like what a user over at VWVortex claims happened when he posted a link to our exclusive 2014 Corvette / 2015 Corvette ZR1 renderings over on Facebook.
I pasted the Jalopnik link on my FB page, and had a very interesting email sent back.
I have a friend of mine who works for GM just email me on Facebook....
"Someone is getting fired over that."
Just a guess here, but it sounds like the drawing is legit.