Green’s Dictionary of Slang

(Aus.) an upstart, a nouveau riche, a general term of abuse.

1919		W.H. Downing Digger Dialects 51: upjump — Upstart; interloper.
1924		(con. WWI) A.G. Pretty Gloss. Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: up jump. Upstart; interloper.