Circular rain cloud observed in rain radar
A way to check if those clouds and precipitation are real is to check the same area and time with another radar.

This is the image loop of Sidney (Terrey Hills) radar for the same time (the same you used). It shows the same pattern than your image. In the animated images that arch centered in the radar looks even weirder.

This is the image loop of Newcastle radar for January 17th, which in great part overlaps the Terrey Hills radar image. It shows an arched pattern, too, and with similar radius, but this one is centered in Terrey Hills radar instead of the Newcastle radar.

Therefore, since those patterns are different for each radar, I would say that they are artefacts, and that both radars suffered from the same kind of artefacts.

Interestingly, that kind of artifact seems consistent with the situation explained in dplmmr's comment: if both radar were just scanning an individual elevation angle (the same angle for both radars) and precipitation were just in a range of heights, we could expect that kind of pattern.