The stomach discomfort
could be from undercooked salmon or may be because of ingestion of plastic vapors.Was the fish cooked properly ? or you just took it out uncooked once you smelled the plastic fumes?
It depends on what kind of plastic material was your spoon made of. I don't think the vapors could have gone through the foil.
But still the cause needs to be ruled out .
You did not mention who else ate the salmon other than your husband.If its due to the vapors of burnt plastic others who ate the same fish can also have stomach discomfort, What about you,? didnt you eat the fish?
If no one else is sick after eating the fish, then your husband must have had preexisting stomach upset
which just triggered by the fish.
Go to your family physician and get your husband examined.If the problem is due to the plastic vapors he needs symptomatic treatment.