Albeit in a medium helo; I have arrived at DH, had the runway environment visual, elected to land and then had the vis subsequently deteriorate in drifting fog. I realize I don't have to tell most folks here that there is no guarantee that the quality of what you can see at DH will continue to the threshold. Perhaps that is the case here.
I "grew up" in a flying community where the older pilots used bad weather and maintenance days to drink coffee and talk about tight spots they got into and out of thus allowing us sprogs to learn from their near-fatal mistakes. I suspect that their candour and professional courage prevented a lot of accidents, the number of which sadly cannot be quantified.
It would appear that we won't have the opportunity to learn from this incident in the same manner which is a pity, as most CFIT lessons are tempered by speculation and can't benefit from a first hand perspective from the cockpit.