I seem to recall a huge long thread a few years back on what differentiates a wagon from a hatch. The consensus seemed to be windows behind the rear door and slope of the rear roofline and window as the differentiating factors. A wagon has a vertical or near-vertical rear window and a straight roof - a hatch has a sloped roof and steeper rake on the rear window.
*shrug*
I'd never call my Fit a wagon, but by that logic, it would be. So really I have no idea... it's all marketing speak anyway, isn't it?