difference between calling method as static and as class method through reflection

It's not using reflection at all. The getResource(String) method called in your first snippet simply isn't declared on ConfigurationManagerUtils - it's declared on the Class class, as an instance method. If the second code snippet works as well, that's because there's a static getResource(String) method declared in ConfigurationManagerUtils (or a superclass). That may well do something entirely different to Class.getResource().

The first snippet is just using a class literal (ConfigurationManagerUtils.class) to obtain a reference to a Class instance on which it can call the getResource(String) instance method.