Personally, I view Space Opera more as fantasy within space, but I suppose it is up to multiple interpretations. I’ll accept Wikipedia’s term.
So if Space Opera is indeed Science Fiction, why didn’t Lucas say so? Why did he say a sentence earlier that it was not Science Fiction. Perhaps Lucas (like me) misinterpreted Space Opera and meant to say fantasy (which is what he went on to explain later in the sentence).
Well, we know he was influenced by Dune, a space opera. And both Flash Gordon and Buck Rogers would be considered space opera in modern genre classification. And I believe he was also influenced by Foundation (galactic empire, a corrupt emperor, and quite a few other things), probably the most significant space opera of the mid 20th century. So I think he knew what he was doing, but he also knew that when a lot of people think science fiction, they think 2001. He was being clear that his creation is more fanciful. More of a classic adventure that only lightly adheres to physics. And he drew from mythic source for his story concepts. He didn’t want movie goers to think boring science fiction. But to publish the story who did he go to? Del Rey, the biggest science fiction imprint in the industry. He wanted the wider audience, but he wanted the science fiction fans as well.
I consider Lucas using the word fantasy as accurate as I do his claim that Vader was always going to be Luke’s father and Luke and Leia were always brother and sister. We know he plays loose with the facts to suit his needs. I think he knew fully that he created an iconic science fiction franchise, but he didn’t want it confused with 2001, the last great science fiction movie that came out. He wanted it to appeal to a wider audience than a typical science fiction movie. Just look at the difference between Star Wars in 1977 and Star Trek The Motion Picture in 1979 in terms of budget an box office. Star Trek had a larger budget but took in a fraction of what Star Wars did.