Main difference in geometry, is freestyle bikes tend to have shorter rear triangles. Gearing is roughly the same, but usually done with smaller gears on the freestyle, to keep the drive train out of the way during grinding type tricks. The freestyle bike will also have U brakes, rather than the race bike's V brakes.

If he's going to be riding it on trails, the freestyle bike might need the tires changed. I think most of them come with street specific tires. Of course, some of the race tires these days look more like street tires, despite being meant for use on dirt.