Black Wallabies (aka Swamp Wallabies) (Wallabia bicolor) are widespread. Many of them look quite like BTRW (Petrogale penicillata) especially when motionless. They have often been mistaken for BTRW. I think the only Rock Wallabies in our region are behind fences at Tidbinbilla/Jedbinbilla.
But if some BTRW had escaped from the enclosures at Tid, would they know immediately and would they tell us straight away? Not necessarily. So there is always the thinnest of faint chances that a BTRW-like Black Wallaby sighting was actually a BTRW!
Thank you Don, I am certainly no expert in this area. It was the compact size and long brushy tail that made me suggest BTRW. I realise it would be an unlikely place to sight one. Always happy for corrections or suggestions.