Green’s Dictionary of Slang

(Aus. prison) a mysterious or private person; a ‘closeted’ homosexual.

1984		B. Ellem Doing Time 129: [I]t’s [i.e. an individual’s sexual preference] kept reasonably well hidden. There’s always the smokies the ones you don’t know about.
1990		Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Smokey. A mysterious or private person. Often one who won’t admit to homosexuality.