Yes agreed this is very interesting. In their guide to the reptiles of Victoria, Robertson and Coventry (2019) mention that, in Melbourne, both subspecies have now established wild populations that originated from the pet trade. Before that water dragons were not known from the Melbourne region. They note that hybrids are starting to be seen along the Yarra River.
I concur. Another sighting of this subspecies has been made nearby. Intellagama lesueurii lesueurii (Eastern Water Dragon) I suggest that some lizard-friendly action is taken before hybrids start to be seen here as well. Local wildlife authorities should be informed of these escaped/released pets.