As your definition states: "Supplier" means a person or corporation, other than a public utility, who sells propane and arranges for its delivery to the operator's tank.
I cleary states OTHER THAN A PUBLIC UTILITY. You can try to spin doctor it, but FerrellGas Retail operations are not a public utility, they don't have a rate base, they aren't granted a monopoly. They supply a product that is often used as an alternative to natural gas, which is typically supplied by a utility.
If you don't like FGP's prices, you can shop around. Now, granted, consumers are protected against predatory "bait and switch" shennanigans and other misleading actions.