The Return of the Jedi novelization introduced the term "jizz-wailer" to describe a musician, but the term "jizz" as the name of the musical style was not introduced until the publication of Tales from the Mos Eisley Cantina, twelve years later.
The original RotJ novelization was released in 1983. Don't discount Legends!
Etymology is not destiny, and in particular Jazz was established before the sexual meaning of the root was firmly (hehheh) established.
Nah, man, Lucas clearly just wasn't familiar with the term and let it slide with the original ROTJ novelization, or the 1984 reference book, or wherever it was that it first popped up. Well, that, or they were just trolling us all along. 🤣