Override is not used

Question

In this program keyword override is not used. In my view ToString() method is not used therefore override is not used. I wish to know whether my understanding is correct. Problem is highlighted.
http://msdn.microsoft.com/en-us/library/ms173116.aspx

using System;

class Person
{
// Copy constructor.
public Person(Person previousPerson)
{
Name = previousPerson.Name;
Age = previousPerson.Age;
}

//// Alternate copy constructor calls the instance constructor.
//public Person(Person previousPerson)
// : this(previousPerson.Name, previousPerson.Age)
//{
//}

// Instance constructor.
public Person(string name, int age)
{
Name = name;
Age = age;
}

public int Age { get; set; }

public string Name { get; set; }

public string Details()
{
return Name + " is " + Age.ToString();
}
}

class TestPerson
{
static void Main()
{
// Create a Person object by using the instance constructor.
Person person1 = new Person("George", 40);

// Create another Person object, copying person1.
Person person2 = new Person(person1);

// Change each person's age.
person1.Age = 39;
person2.Age = 41;

// Change person2's name.
person2.Name = "Charles";

// Show details to verify that the name and age fields are distinct.
Console.WriteLine(person1.Details());
Console.WriteLine(person2.Details());

// Keep the console window open in debug mode.
Console.WriteLine("Press any key to exit.");
Console.ReadKey();
}
}
// Output:
// George is 39
// Charles is 41