Paul - The Census of Vascular Plants of the ACT does not list wong wonga vine as occurring in the ACT, and I have only seen it growing in the Botanic Gardens. However there is a 1927 record from about the Bass Gardens area and it is listed as an uncultivated record. Wonga Wonga does also grow naturally in the NSW vicinity, so could be a significant sighting rather than a garden escapee. Did you notice any Wonga Wonga Vine growing nearby in a Garran backyard?