Because it comes with the "no glasses" 3d so staring at the screen from a fixed distance from a fixed angle you can see the 3d effect. In reality it's basically 2 layers of screen. It also has a 3d/2d switch and a 3d camera, following the hype, just like any other 3d phone.
Now if you wanted my opinion I played with the 3D LG phone and I think it sucks. It's not "wow, awesome" kind of thing though, like they want to make it seem like it's the new cool thing. As much as I think that 3d tvs kind of suck I think that 3d phones suck much more.