为什么Groovy Overridable中的（Java）公共方法？

Question

public class JavaClass {
    public void echo() { 
        System.out.println("Echo'd from Java Class"); 
    }

    private void doSomethingElse() {
        System.out.println("Something else happening from Java Class");
    }
}

通常在Groovy中，(Java) private methods cannot be overridden。但是，似乎可以像下面那样覆盖公共方法：

JavaClass pojo = new JavaClass()
pojo.metaClass.echo = {
    println "Echo overridden!"
}

pojo.metaClass.doSomethingElse = {
    println "This won't be overridden"
}
println pojo.echo
println pojo.doSomethingElse

输出：

Echo overridden!
Something else happening from Java Class

如果无法覆盖私有方法，为什么允许使用公共方法？