The cause of this incident could be determined within an hour of it occurring. If it's investigated you'll find out the cause in about 3 years or so.
But it probably won't be investigated by CASA or ATSB and won't need to be. Both the student and instructor will be better pilots having experienced this, I know one dude (instructor) who had a similar experience, was exceptionally well treated by CASA (fairly) and now fly's an A320 for a major airline. That the student walked away from this is a job well done.