This optical illusion is called forced perspective, which was one of the techniques they used in Lord of the Rings to make the hobbit characters look very small. I had learned about it years ago in an art class, but the behind the scenes documentary on one of the DVDs really made the concept make sense to me, so I thought I'd give it a try.
Jay's actually kneeling about ten feet back from the drum kit, but the angle covers that up. The compression effect of a two-dimenional medium, along with color correction in Photoshop gives the illusion of a tiny-sized Jay bashing away at the drum kit. The super-sized drumsticks helped the illusion as well.
If I were to retake this photo, I would have had Jay kneeling back further...the sticks are too big for the scale of the drumkit. Still, considering how quickly I put it together, I think it came out kind of nifty.
By the way...I heard the demo today. It sounds great!