We came up with the idea of hiring a 3D artist to do a "fantastical" screenshot after being impressed with the "cool factor" of apps like Angry Birds.
Angry Bird's first screenshot is NOT actual gameplay at all, but rather an artistic representation.
Our screenshot has been through a LOT of iteration to get it to look impressive, but we don't want to deceive our customers. On the other hand, we figured that if the Angry Birds customers were okay with it, our users -- who are very techy in general -- would be cool with it. And we've had some version of that shot in the App Store for over two years, and this is the first complaint. Furthermore, you're not saying you bought the app mistakenly, but just worried that we're deceptive.
We'll definitely meditate on how to resolve this confusion for the next release (we are not allowed to change shots in between releases). Perhaps a disclaimer on the shot might work to avoid confusion, too.
Thanks for your concern!