I think the phrase “ external” used by the Russians referred to an outside actor and means of destruction, not anything “ internal” such as mechanical or human failure
They were not referring to an external explosion
At least some of The wreckage showed metal peeled from inside out indicating internal explosion
31k feet destruction is an unusual destruction altitude but has been noted an at least 2 other prominent terrorist bombings, including PanAm 103 and I read also Air India ..... Poss indicating barometric bomb
Russian airlines has a poor safety record.