Engadget claims to have confirmation from the photographer but really you can't make anything out in the picture. It could be anything. And so what, I mean _I_ still don't have one. And thats all that really matters right?
And if you read the linked article, it says it was taken on caltran, which could also increase the odds of legitimacy. The person who took it reported back to Engadget saying he saw him using it, and it was definitely an iPhone.