What is the technology here(IEnumerable)?

So for the method

public static IEnumerable<object> AllParents(object obj)
        {
            while (true)
            {
                obj = GetParentObject(obj);

                if (obj == null)
                    yield break;

                yield return obj;
            }
        }

Is it implicit or explicit implement? I suppose

Implicit Interface Implementtation

public class MyClass : InterfaceOne, InterfaceTwo
{
    public void InterfaceMethod()
    {
        Console.WriteLine("Which interface method is this?");
    }
}

interface InterfaceOne
{
    void InterfaceMethod();
}

interface InterfaceTwo
{
    void InterfaceMethod();
} 

Explicit Interface Implementation

public class MyClass : InterfaceOne, InterfaceTwo
{
    void InterfaceOne.InterfaceMethod()
    {
        Console.WriteLine("Which interface method is this?");
    }

    void InterfaceTwo.InterfaceMethod()
    {
        Console.WriteLine("Which interface method is this?");
    }
}

interface InterfaceOne
{
    void InterfaceMethod();
}

interface InterfaceTwo
{
    void InterfaceMethod();
} 

But my method's format doesn't match either of one.