In my opinion you are not in a public place or open to the public when you are within your Lot on your balcony. If you were in your front garden of a suburban Lot rather than your back garden it may be a different issue.
“To sustain a conviction, the prosecution must prove beyond a reasonable doubt that you had the requisite intention to expose yourself, and that it was in or within the view of a public place or school. As this is a summary offence, the matter will be heard and finalised in the Local Court.
Exposure in the context of the Act refers to the revealing of your genitalia in a public place. This can include exhibitionism or public nudity, and there is no requirement for a sexual act to be performed. Examples range from streaking at a public sporting event to flashing genitalia to a partner in a public place. A public place for the purpose of this section is taken to mean a place that is open to or used by the public. It is not necessary for someone to have seen the exposure, but instead the focus is on whether the offender has or should have a reasonable belief that others could see the transgression. This law is based on the belief that obscene exposure goes against accepted community standards.” (my emphasis)
– See more at: https://criminal-lawyer.com.au/obscene-exposure-lawyers-sydney/#sthash.ZEL5wo55.dpuf