Rottenray, you make a good point! I read the report yesterday and now that I re-read it again I agree it is not stated as such. However, the ATSB do use the term 'disc burst' so I think my interpretation was tempered by that. Discs 'burst' through overload, so whether that overload was caused by overspeed beyond it's design limit, or being weakened by the fire and then failing at a lower limit becomes a little academic once the bits start flying out the side. This was more the point I was trying to make regarding the use of the word 'explosion.'
Apologies though for any misleading suggestion.