We don't require that a lens *focus* light, only that it bend light, as you said. From optics, a concave lens disperses light, sending it out at wider angles than it comes in. From astronomy, other examples of lensing include cases where a single image is broken up into multiple images, or is smeared out into a distorted version of the original. A common lensing effect is our ability to see more than 50% of the surface of a spherical body because light from just past the horizon is bent in our direction.

As far as the shape of the gas cloud plays in, the total mass and the center of gravity of the cloud are the primary concerns in determining lensing. As long as the cloud is sufficiently compact, the shape only slightly changes the otherwise spherical distortion of the lensed images.