To me, the only real question is "why were they so low?".
Form the recent Polish media reports, these pilots were known to be very "by the book" types. The idea that they were trying to duck under the fog to find the airport is absolutely unacceptable, especially that they were fairly familiar with the airport and its topography - they must have known about the valley before the runway threshold.
However, the early indications are that they were in a rush. This leaves room for mistakes, especially when using a language foreign to them for communication, perhaps they thought they were given QFE while actually it was QNH? Perhaps they misunderstood one of the digits and their mistake was not caught by the controller? The controller claims they were not fluent in Russian, especially numbers, their superiors claim the opposite. Perhaps in a rushed situation there was a misunderstanding. I am no expert here, but could someone post a likely descent profile if the wrong setting was used? Would it be at all similar to what we have seen so far reconstructed? How much of a difference is there in the QNH-QFE settings at Smolensk?