This, from what I can tell, was at least mostly untrue. The woman who helped create most of the technologies, Adele Goldberg, stated on film more than once that she _strongly_ opposed showing the Apple team anything, as she knew they would just take the technology (in return for giving Xerox the _opportunity_ to invest in Apple, wow, what an incredible deal /s). She specifically said that she would NOT give the tour unless ordered to in writing, and her boss did indeed write that order.
So she and her team very reluctantly gave the entire GUI desktop concept away for free. Not to mention they also demonstrated object-oriented programming and a networked office, things that Apple (and NeXT) would capitalize on later as well.
In later years, Jobs even admitted as much -- he said Xerox could have been IBM or Microsoft. They had everything needed to start the home computer revolution but squandered it. While it's true that Xerox execs didn't want to market the research done at PARC, and they wanted to focus on their very lucrative copier business, that doesn't mean they had to give the technology away!