I'm posting this because to me it seems very plausible, plus the source is one I trust and have trusted with my life.
I had a rather enlightening conversation today with said source who from another friend who is in a similarly senior position in a relevant and related business has heard the following, and I paraphrase:
The sequence of events leading to this tragedy appear incredibly trivial: Two young F/O's left at the controls, discussing a two day layover in Rio with a couple of flight attendants present on the flight deck (most PAX asleep), are completely unaware of where they are headed weather wise.
Sad if that's what led up to this, and a serious self management challenge...