This cat remains ghostly after it is tamed! To summon a Ghost Saber you have to find and click on Cat Figurines around the Ruins of Mathystra, until one appears.
Level scaling: In Shadowlands most NPCs will scale with the Hunter's level, within the constraints of their level range. Hunters can tame regular NPCs up to 2 levels higher than them, but can only tame elite NPCs of the hunter's level or below.