Pet peeve: This is a common misunderstanding. Focal length doesn’t cause the distortion. The distortion is caused by the distance between the camera and the subject. Think of longer focal length as an optical crop. A longer focal length allows you to be farther away from the subject while still filling the frame. If you took a photo from the same distance with a wider lens and simply cropped it afterwards to have the same composition there would be no difference in distortion.