Objective-C message passing related queries

Question

I am learning objective-C after having good knowledge of C/C++. I have 2 questions:

1. Are Obj-C message passing and C++ vtable, two different ways of implementing polymorphism or Are they two very different concepts which I have misinterpreted into different implementations of same concept?

2. I read following line from this pdf http://www.gnustep.org/resources/documentation/ObjectivCBook.pdf

   Polymorphism takes a pluralistic point of view and notes that several classes can each have a method with the same name. Argument overloading takes the point of the view of the method name and notes that it can have different effects depending on what kind of object it applies to

   In essence both do what we want from them i.e. calling method according to the object. What is the difference then?