What causes Distortion ?
Wide angle lenses by themselves do not cause distortion but when used too close to the subject, it appears distorted.
Wide angle and Distortion
when photographed with a wide angle lens, the car in the end at the extreme left appears very small and the bonnet of the first car is kind of protruding out unnaturally. More of the top of the bonnet is visible.
when photographed with a long focal length lens, the same car in the end at the extreme left appears larger and quite closer. The bonnet of the first car is as it should appear naturally. Less of the top of the bonnet is visible. All cars appear to be parked much closely and there appears to be less difference between the cars.
This happens naturally with the human eye as well. As one walks closer to the benches, one is able to see more of the top surface of the bench when photographing them with a wide angle lens. For an almost same composition, one needs to walk back to shoot it with a telephoto lens. As a result less of the top surface is visible. Also the benches appear closer together in case of a telephoto lens compared to the separation visible in case of wide angle lens
If you look at this photograph, you do not really see the distortion and the photograph appears quite normal except when you notice the curved verticals at the extremes. Shot with a fisheye, the distortion is only there over the areas which are closer to the camera.
The celebrated chef has been photographed with a wide angle lens. The distortion is not visible except for the extended hand or the plate closer to the camera.
Not really a distortion but the use of a wide angle creates more impact.