Curious Question about ProgressBar object between two classes

In FirstWindow class:
* Has progress bar object named "progressBar1".
* Its value is updated in this class as the process runs.

In SecondWindow class:
* Has progress bar object named "pbSecond".
* This SecondWindow class invokes FirstWindow class but does not use (display) the
FirstWindow GUI.
* This SecondWindow sends the data to FirstWindow the data to be processed and save to the file.

Now, I had this kinda of crazy idea to try and was amazed it does work! I'm not certain on how this works... passing the pointer of the object?

FirstWindow class has this property:

public ProgressBar pBar
{
set { progressBar1 = value; }
}

public int DumpRFData(byte[] dat)
{
pBar.Maximum = dat.length;
for (int i = 0; i < dat.length; i++)
{
progressBar1.value = i;
... code sippet (for retriving dump data)
}
}


now in SecondWindow class:

public int DumpData()
{
byte[] data = new byte[1000];
FirstWindow fw = new FirstWindow();
fw.pBar = pbSecond;
fw.DumpRFData(data);
}

when the DumpRFData is invoked, the progress bar in SecondWindow is updated as the process in FirstWindow runs.

How could that be happening? Processed from the pointer or what?