how they ended up in a CB IN THE FIRST PLACE,would most likely be ,the blame of the weather radar.To me 10 000 fpm descent, might have been aided with the CB downdraft.
There is no evidence to even slightly suggest that they were in a CB. In fact, based on the statements in the report (the call to the cabin, the 12° left turn, the decel to M0.8) they knew very well what was going on with the weather and were steering around the worst bit. IMO they were obviously not in a CB, but in cloud in bad icing conditions.