I had my doreensis and crispa for 5.5 years, and fed silvers once a week for the last 4 years and never had an issue.
But my other tank, nem species w/ 3 LTAs were fine until that particular feeding, and all 3 did the same thing, no other changes, so reason for my conclusion.
Immediately after this I placed 3 BTAs in tank and they were fine, so I can't say anything wrong w/ the tank/water column itself.
I do agree, there is always a chance of something else that caused this, but again, plenty of other food choices, not worth the risk IMO.