George Lucas was actually a friend of Joseph Campbell's.
He considered Campbell his mentor, and Campbell consider Lucas to be somewhat his student.
When Bill Moyers shot "The Power of Myth" (which is how most laymen came to know of Campbell) he shot it at Lucas's Skywalker Ranch, with Lucas's invitation to do so.
I'm a huge fan of Campbell's, and in fact feel that if more people read him, we'd probably live in a much better world.
The depth of Campbell's intellect is impressive, and George Lucas (for any who have ever watched him interviewed) is actually a bit of a dummy.
That Lucas read and understood "The Hero's Journey" isn't really impressive, as it's really not that difficult to understand Campbell's basic points...........but Lucas did indeed turn what is an amazing tale of the history of mankind into a Saturday afternoon movie serial.
I believe Lucas has a bit of a low IQ, and that his take on Campbell's "Hero" resulted in Star Wars is hardly surprising.
In effect, it was the best a guy like Lucas could come up with.......and not very good indeed.
Even though Star Wars is often the film mentioned as an example of "The Heros Journey", there are dozens of far better films which use Campbell's template to far better effect.
An interesting take on how Campbell's Myth's have impacted almost every great movie out of Hollywood can be found in Christopher Vogler's book "The Writers Journey - Mythic Structure for Writers". A fantastic read if you're at all into the works of Joseph Campbell.