The nearest what seem to be natural records for this species are Rye Park and Wallendbeen. There are two records from Black Mountain but not sure if these are in the Botanic Gardens. Silke it would be good if you could take a specimen to Dave Albrecht at the CSIRO herbarium
It's definitely Eremophila debilis, and has certainly been planted on quite a few occasions at ANBG. The species is often cultivated and is most likely an 'escapee' from a garden, probably via birds dropping fruit. A stem with leaves and a few fruit would be sufficient for a herbarium specimen for Dave Albrecht.