Well that's the thing, GG didn't actually make the game, an indie dev that liscensed Garage Games' engine made the game. And this is the exciting part. GG is at the forefront for empowering indie developers with their super cheap liscensing of the Torque engine ($100/liscense which is peanuts for what you get). This had made them the biggest indie dev community which means TONS of support and documentation, for a professional grade engine. Now, what this announcement means (and some other stuff I've read) is that the Torque engine has been ported to 360. This is awesome because devs can just code for the Torque engine like normal, and if their game is good enough then I'm sure an agreement will happen with the GG guys who'll then port their game to the 360.
I don't know the details and whether or not GG will supply dev kits to the developers, or how the whole porting relationship will work, but GG has shown that they've very reasonable. I'm extremely excited and interested to see just how well XBA does in regards to selling indie games, because if they make a lot of money out of it, then there'll be far more incentive for indie devs to make their games even better. And with the potential of increased revenue, will hopefully be easier to find funding for their projects.