What you are describing is properly known as tilt. What it means is that the optical axis of the lens is not perpendicular to the plane occupied by the camera's sensor. In your case the entire lens appears to be tilted relative to the camera's lens mounting flange.

Just look at the adapter plate. The right side in the photo is significantly closer to the focus ring than the other. With wide aperture wide angle lenses misalignment of as little as 20 microns can be seen when used with high resolution sensors. In this case we can eyeball the difference from several inches or even feet away! As it sits the lens is flat on the table and the adapter plate is crooked. But once the lens is attached to the camera, the adapter plate will be square with the camera and the lens will be pointing at a slight angle.

There are specialized lenses that intentionally introduce such angles between the image plane in the camera and the optical axis of the lens. They usually include tilt movements as well as shift movements. Thus they are called Tilt/Shift or Perspective Control lenses.

Just as an aside, a decentered lens element is, in some ways, similar to a shift movement using a T/S lens. The biggest difference is that all of the elements in a T/S lens are moved together and the various pieces of glass stay in the same alignment with respect to the others. When only one lens element moves in a direction perpendicular to the optical axis of the lens it results in degraded image quality because it is no longer aligned with the other elements in the lens.

You could also get the same result if the camera/lens system is perfectly self aligned but the entire system is improperly aligned with the test chart. The sensor and test chart must be parallel to one another or one side of the chart (or the top, or the bottom, or one of the corners) will be closer to the camera than the other. This will result in only one part of the chart being in focus at any particular focus distance.

For a good explanation of the difference between decentered, tilted, and mis-spaced lens elements (with illustrations) and how to test for each, please see Roger Cicala's excellent blog entry titled: Testing for a Decentered Lens: an Old Technique Gets a Makeover