Is that with your thumb on the bottom of the disc and fingers fanned on top?
If so I've heard it called a "caveman" throw. It's useful for ultimate since,
1.) It's an unexpected throwing motion, so tough to defend.
2.) You don't have to re-grip if you catch the disc with your thumb on the bottom, so it can be a very quick catch-to-throw transition.
I've only ever seen one person consistently throw a golf disc in that style: Glen Whitlock (#3513). He could place them pretty well in the 250-300' range, but it just looked super weird.