Could it be that you are sensitive to buckwheat itself?
It's related to rhubarb if that helps.
Probably the Curry Mix as it is a mix and they do put something in with the herbs to keep them from sticking although less and less is that wheat derivative, I've seen a lot of rice starch used for this application.
I'd find another way to make your dish, not using this curry mix first and see then if you react again.
Buckwheat in a pure flour should not cause a problem for most folks, it isn't related closely at all to other non-gluten grains.