Why does Star Wars say "a long time ago, in a galaxy far far away?" Besides sounding like a fairytale beginning, does it have any literal truth in the series or the canon?

I mean, humans prominently feature in Star Wars, and humans on earth today have only recently evolved technology to go to nearby planets. How does the Star wars franchise explain this? Are those humans somehow in another galaxy before advanced humans evolved on earth, something like out of Battlestar Galactica?

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