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, if they descended to elevation plus minima 830 & 330 = 1160 thinking it was QNH, they would have been 1160 above the airfield, not much chance to get the lights , but equally no chance to hit the ground.
What would have killed them would be descending to a minima (330 MDH?) based on QFE thinking it related to QNH (and having set it as a QNH MDA and having set QNH if one was given, which I doubt) .
This of course would require total absence of thought concerning the field elevation.
I think they will have operated enough in soviet bloc countries to be familiar with QNH/QFE/Metres Feet confusion, but well, under pressure I guess anything is possible.