In Joker Squad of the New Galactic Empire stormtrooper corps' 407th Division, an unseasoned recruit was pejoratively labeled a noob, presumably a slang abbreviation of newbie or newcomer. Whether the term was used in the wider stormtrooper corps or even the Galaxy at large is unknown.
When Anson Trask was promoted to Joker Squad in 137 ABY, he acquired the moniker, which ironically saved him from the retribution of Darth Maleval when Trask annoyed the Sith Lord. He would outgrow the title in the eyes of his peers after he later shot and killed Maleval.
The word may have been derived from the term newbie, a Gungan slang term with a similar meaning that enjoyed galactic notoriety.
I agree with Yossy.... Maybe the creators kid was using the word.