That's correct. You shot your images under an incandescent light, yes? Incandescents throw a yellow light; the camera assumes that the light is white, so everything you shoot under that light gets a blue cast to it. By telling the camera that the object you're pointing it at is white, it adjusts for the color temperature of the light.

You can do the same thing in the photo software, but it's simpler to do it in the camera, usually. If you're shooting in RAW mode, though, it doesn't matter--RAW doesn't store any of the in-camera processing. In that case, you'll have to do the white balance in the software.