You're confused because the author is using terminology that is more common outside the Ducati superbike world.
Ducati superbikes, unlike a lot of bikes, have a rear ride height adjuster that (more appropriately) should be called an attitude adjuster.
It's purpose is to change the bike's front-to-back height relationship thereby changing the steering head angle, the height of the center of gravity and ground clearance without also needing to change the forks position in the triple clamps.
This allows you to independently raise the front and the back of the bike equal amounts for ground clearance and to raise the C.G. for better cornering, or to raise the rear and drop the front equal amounts to change the steering head angle to quicken the steering. So its adjustment gives you more control over the chassis geometry, making it easier to affect handling objectives.
(Keep in mind that lowering the front ride height or raising the rear ride height are not equivalent adjustments. Lowering the front serves to lower the bike's center of gravity. Raising the rear raises the C.G.)
The rear ride height is set at the factory to obtain the proper chassis geometry, where chassis geometry is defined in terms of wheelbase, fork and steering head angle, ride height, weight distribution and wheel alignment.
Suspension, on the other hand, is defined in terms of spring rate, damping and wheel travel.
When you move outside the Ducati community and you talk about changing ride height, you're talking about setting how much of the suspension stroke will be available for absorbing bumps and how much travel will be reserved for extending the wheel into a drop in road contour.
Here, the ride height is being called the distance to full suspension compression. The distance to full suspension extension is called sag. Increasing spring preload reduces sag and increases ride height and vice versa.