It's the other way round ... a 4:3 picture is cropped at the top and bottom to fill a widescreen TV.
Alternatively they may be using a 'smart' algorithm which keeps the centre of the picture in the correct aspect ratio but stretches the edges to fill the screen. This works quite well, since we tend to concentrate mainly on the central portion of a widescreen TV, but can look a bit weird if the camera is panning slowly across a scene.