You witnessed an argument between Gems, which quickly led to a heated one, and resulted in one for the Gems getting shattered. When the Gems get in their spaceship and leave, you inspect the Gem's remains, only to find a purple pistol, and pick it up.

Oh thank the Stars! I'm in a better person's hands!

The gun spoke, turns out this pistol is a Gem! Somehow forced into a weapon frame.

Name's Magenta Quartz! You can just call me Magenta!