Question

mybox.Checked := true;

Setting TRadioButton to checked (by code) causes OnClick event handler to be called.

How can I recognize if user is making the state change by GUI interaction

Answer 1

You can nil the OnClick event handler while changing a radiobutton state programmatically:

procedure TForm1.Button6Click(Sender: TObject);
var
  Save: TNotifyEvent;

begin
  Save:= RadioButton2.OnClick;
  RadioButton2.OnClick:= nil;
  RadioButton2.Checked:= not RadioButton2.Checked;
  RadioButton2.OnClick:= Save;
end;