[Lazarus] VirtualTreeView, Absoluteindex example on freepascal.org

[Jürgen Hestermann]

On
http://wiki.freepascal.org/VirtualTreeview_Example_for_Lazarus
there is the following example procedure:

------------------------------------------------
procedure TForm1.Button1Click(Sender: TObject);
Var
   Data: PTreeData;
   XNode: PVirtualNode;
   Rand: Integer;
Begin
   Randomize;
   Rand := Random(99);
   XNode:=VST.AddChild(nil);

   if VST.AbsoluteIndex(XNode) > -1 then
   Begin
    Data := VST.GetNodeData(Xnode);
    Data^.Column0:= 'One ' + IntToStr(Rand);
    Data^.Column1:= 'Two ' + IntToStr(Rand + 10);
    Data^.Column2:= 'Three ' + IntToStr(Rand - 10);
   End;
End;
------------------------------------------------

Can someone explain what the line

   if VST.AbsoluteIndex(XNode) > -1 then

actually means?
The method AbsoluteIndex gives back a Cardinal so how can it be less than 0?
Therefore the if statement is completely useless because it is always true.

BTW: I was pointed to this because Lazarus (or FPC?) showed me a compiling
message that this line will cause a type convertion to 64 bit (well done!).