See my other comments in the other threads. This does not have EDAC. I was as surprised as you but it doesn't seems to be an MCU but a composition of several distinct chips. That flight computer was designed in the 90's and updated in 2002 with a new hw variant that does have edac. So yes, for this kind of thing, I can buy that a bit flip happened.
You can see much more data in the report:
https://www.atsb.gov.au/sites/default/files/media/3532398/ao...