Moroni is a notoriously difficult airfield to fly into, especially at night. The airport is at sea-level on the West side of a skinny island, with a 7700' mountain just to the southeast of it and a 3600' one to the northeast..
There is no published approach to Rwy 20, just an VOR/DME/ILS for 02.
Easy to get disoriented at night as there are very few ground lights, a true 'black-hole' with part of it being the volcano mentioned.
Think SAA had a daylight-only policy for Moroni. No need to look further than CFIT and/or disorientation for this one IMHO.
Another sad day for us all.