To answer the question, Ultima Shadow is having incredibly good luck.

The probability of which finisher you get is based on the gunblade you're using. Lionheart gives a 25% chance to activate any of the four finishing moves and is the only gunblade that will allow you to use Lionheart Finisher as well. Crisis Level only affects whether Squall will activate a finisher.

What's interesting though is that every gunblade that isn't Revolver or Lionheart gives a higher percentage change to activate their strongest finishers. So Shear Trigger and Cutting Trigger give a 75% chance to use Fated Circle, while Flame Saber, Twin Lance, and Punishment give a 50% chance to activate Blasting Zone. Revolver meanwhile can only do Rough Divide, whereas Lionheart does the even split.