I don't think this is Cassinia quinquefaria. The leaves are far too short, and the seed-heads look different. See this example: Cassinia quinquefaria (Cassinia) on 5 Aug 2018
Quinquefaria leaves can be 2 cm long. You are probably right about the flowers looking different in seed, though there seems to be a fair bit of variability. Plantnet says the pappus is up to 2.5 mm long, so it should not look as fluffy as in this photo. On the other hand, I don’t think it looks like Cassinia sifton or Cassinia aculeata either and I cannot think of anything else.