Perhaps I am being thick here but, assuming they had set the correct number of Hpa given by ATC there was no danger associated with believing they had set QNH when in fact it was QFE,
Or it could be the opposite.
But those are all just guesses.
We now, that visibility was below minimal and as for now, almost sure, no technical problems. It would mean CFIT. Now, what were the causes? Weather. That's for sure. What else?
On the russian PM website there is a transcript of a discussion of the 11th,
Andrasz, link please.
Arrakis