I would imagine the owners name them.
But how they come up with some of the weird ones is anyone's guess. Some others from yesterday's line-up:
Friesan Fire
Hold Me Back
General Quarters
I Want Revenge
Musket Man
Papa Clem
Nowhere to Hide
Summer Bird
Chocolate Candy
Atomic Rain
Mr. Hot Stuff
Advice
Join in the Dance
Westside Bernie
The Arabs are better at giving halfway decent names to their horses:
Desert Party
Regal Ransom
Dunkirk
Pioneer of the Nile