This is nothing new to the people involved within the trade.
Vietnam has been importing sickly clams for years.
I find it odd that your source claims these are reportedly farmed in Veitnam?
Vietnam collects tens of thousands of wild Tridacna clams each year, there is no market for clam farming , do to the abundant supply of cheap wild stocks of this particular clam.
I would be interested in seeing the outer shell markings of these clams to confirm their cultured origins.