Speculation is good for a numer of reasons.
If someone posts that it hit the other because you can't see up in a Cessna and can't see down in a Piper, I'd read that (as a qualified pilot) and think to myself, "mental note, keep a good lookout next time I'm climbing and turning onto downwind" or similar. Same goes for a numer of other scenarios that sometimes appear here.
On a side note - from news in the USA, a homebuilt Velocity with 5 hours on the taco has crashed into a house in Las Vegas Nevada killing its' 2 elderly occupants who were home at the time. Lets home the near miss in Perth is the third occurence as they say these things often happen in 3's.