Green’s Dictionary of Slang

one who is out of their usual environment; a fool?; also as adj.

1874		Morning Star & Catholic Messenger (New Orleans) 21 June 8/4: The blacks are never called men and women and children. ‘Myalls’ and ‘niggers’ and ‘gins’ and ‘piccaninnies’ seem farther removed from humanity.
[1885		Bulletin (Sydney) 18 Apr. 10/1: This is how Black-tracker Jock chose a wife. It was in the early days, when all the blacks on the Burdekin were ‘Myalls,’ that this matrimonial spec. was ventured on].
1890		A.J. Vogan Black Police 200: Them Myalls (wild natives) don’t seem to mean business to-night.
1904		Sun. Times (Perth) 3 Jan. 10/6: Music that, properly rendered, would charm the soul of a myall black.
[1936		A. Russell Gone Nomad 26: Mulga Jack and I carried a revolver each [...] not that we had any trouble with the myall blacks].
1946		E. Hill ‘Santa Claus of Christmas Creek’ in Rees Aus. Radio Plays 202: That’s your serviette, you old myall!
1951		E. Hill Territory 445: Myall express: Natives to show a traveller the way, or to help.
1954		T. Ronan Vision Splendid 111: All lubras with the slightest vestige of comeliness were taken out of the kitchen and replaced by some weak, half-myall misfits.