Finally from what I know Cambell ended up living on Skywalker Ranch. I see no reason to minimize connection.
Or you could say 'I should stop drinking milk, because I'm somewhat intolerant' and he'd say, 'ahh, yes, you're in the middle of the hero's journey, on the precibus of learning to set your desires aside for the betterment of your health'
Any story with conflict becomes the hero's journey, and what stories worth telling don't have some kind of conflict. 'Proto-story' nonsense.
Either way, I wouldn’t be surprised if Campbell was the one making the connections—between Life of Milarepa (which, in my opinion, is the closest pre Campbell example of the hero’s journey to Campbell’s original framing) and The Wizard of Oz. Meaning the stories all have the parts of the journey but the Life Milarepa has a 1 to 1 correlation.
And Campbell knew a good thing when he saw it, happy to agree that Lucas' film represented a hero's journey.
This was a time when Campbell's writing was entering broad pop consciousness and his speaking engagement schedule was starting to grow: the massive popularity of Star Wars was a great ship to catch a ride on.
People wanted to see a depth in Star Wars that caught Lucas off guard (remember that he just wanted to replicate the exciting, cliff-hanger kids serials of his 1950s childhood). He decided to go with it, saying it was all part of a big plan, "I have ten movies with their stories all plotted out" etc. The reality is he cobbled things together ad-hoc and kind of quickly, with no real overarching intent - something he only decades later finally admitted.
I feel for him: in his mind, he was just a nuts-and-bolts technology guy who loved the "how would I make that?" questions and work far far more than the story he had to come up with to tell. He freely admitted he hated writing. If he had it his way, he would have merely been the head of ILM, excitedly figuring out ways to use new technology to solve film making problems, but Star Wars blew up on him, becoming an over-the-top ultra-success.
The real connection between Lucas and Campbell was nearly non-existent, but it was a useful thing for each of them to strategically latch on to as their popularity began to rapidly grow.