Pre-order Trine on Steam, get Shadowgrounds for free

Usually, whenever we're offered free games as a pre-order bonus, there's some common theme between the reserved title and the aforementioned playable incentive. Perhaps the bonus game is the prequel to the upcoming release, or at least belongs in the same genre as the pre-ordered title. However, a recent deal on Steam seems to go against this convention -- if you pre-order the upcoming fantasy action-platformer Trine on Steam's download service, you get the frantic top-down shooter Shadowgrounds for free.

Okay, so they're both made by indie developer Frozenbyte, but still -- there's a wide chasm between the worlds of Smash TV and ... well, we can't think of a pre-existing game to compare Trine to. Super Ultima-rio Bros?