The term static polymorphism is associated with overloaded methods because it gives the impression that a single named method will accept a number of different argument types. The System.out.println() method is an example that may take String or Object references, boolean and other primitive types as an argument. In fact, each overloaded method is separate and the compiler can see the difference between them. In this case, the argument types are fixed at compile time and are considered static. This has nothing to do with the Java keyword static.
Dynamic polymorphism is where a class overrides a superclass method or implements an interface. For example, any class may override the Object.toString() method and provide its own implementation, and this is known at compile time. However, for a simple Java program that instantiates a series of objects and calls their toString() method, the compiler does not consider the object references differently. Any differences in the objects' toString() implementations are only seen at runtime, so they are considered dynamic.