It was a completely normal "downwind fullstop" call, and according to the available ADS-B data, it appears the pilot initiated the turn on to base at the expected point.
Yes, I had a bird strike on a turn onto final once and it gave me a hell of a startle and sudden attitude change, luckily it was on the end of the wing so not too much adverse effect on the handling and we got down safely, but I agree that a bird strike or a seat rail failure could possibly lead to an event like this.
Hopefully that will put paid to any further speculation about mental illness/sudden incapacitation due medical condition.
I never cease to be amazed at the fact that a pilot's worst enemy is other pilots. Why any pilot would think it's a good idea to stoke the CASA AvMed fire of intrusion and destruction is beyond me.
And that's setting aside the abject absence of any thought or sympathy for the deceased pilot's family and friends.