There’s an entry for it on the ACMA’s register: https://web.acma.gov.au/rrl/licence_search.licence_lookup?pLICENCE_NO=12771555/1
It’s a TCBL scheduled to run until 15 February. The station is “Ahlulbait Radio Australia”. They made a post about their TCBL transmission:
There’s also another TCBL in Sydney at the moment on 91.6 MHz, which is 2CR (Chinese Radio), broadcasting from Centrepoint Tower until 22 February:
I believe it’s the ACMA that chooses the frequencies, rather than the stations themselves. In any case, Move FM on 107.9 is permanently receivable in most of Sydney – no tropo required. It’s also still audible on its Katoomba relay on 99.5 MHz.