You are absolutely wrong. Xerox PARC had the "rough idea" of a GUI, the mouse came from SRI, the concepts of Icons, Menus came from other areas of research at various Universities, etc...
It was "Apple" that refined it, then set the "Standard Interface" we all use today. The Xerox systems looked nothing like Windows or a Mac. It was very rudimentary stuff, at best.
You can deeper into what actually happened here:
Apple did not "rip-off" the Macs UI from Xerox. Apple had hired some people from Xerox (like Jef Raskin, Bruce Horn) who believed in concepts of a Graphical User Interface. These concepts are pretty broad -- like making a computer easier to use by using graphics (icons), using menus, windows and making a consistent interface to do things. The work on these concepts predates Xerox PARC -- in fact it was many of these peoples individual work on those concepts that got them hired at PARC. So Xerox (PARC) brought them together to refine them.
More...
http://www.mackido.com/Interface/ui_history.html