An email on this issue:

I have been trying to raise interest in this issue with the people at ProMED since last May, after I found out that FAO had funded fishfarming projects at Qinghai Lake some years ago and that there were probably still fish farming operations there that could have been involved in the outbreak.

Additional information of possible interest on this issue:
(1) Excessive use of poultry manure to fertilize lakes and reserviors has been cited as the cause of mass die-offs of farmed carp in China involving hundreds of thousands of fish [apparently from oxygen starvation].

(2) raw chicken entrails and unprocessed offal are used in Thailand as fishfeed in snakehead farming (“With the expansion of the poultry processing industry, chicken entrails are also becoming increasingly available …. Some farmers use this new feed resource exclusively for feeding snakehead in ponds”
Consultancy Report for the Initiation of a Programme for Fish Feed Development in the Regional Lead Centre in Thailand ).

[latter is on FAO website]

So, poultry entrails and offal fed to fish…
And if a farmer suffers sudden die off among number of birds – might it be tempting to not tell authorities (get trouble, maybe all birds slaughtered and may wonder if will be compensation), instead get a little money selling for fish feed?