Food stamps can only be used to buy ingredients and raw food, not cooked food, and therefore can't be used in restaurants.
Some people with food stamps may not be able to cook food - e.g. broken stove, no stove, lack of electricity or gas to stove.
Seafood markets are primarily sellers of raw food. They therefore take food stamps.
Many seafood markets in the U.S. southeast will also prepare and cook food upon request. Officially this is a side service.
Some friends of mine (formerly the owners of a Chinese takeout) own and run a seafood market. It's located in a poor part of town. They will fry, steam, or boil nearly everything they sell (for a small fee).
The end result:
There is no actual difference between their seafood market and their Chinese takeout from an order-taking/food-passing perspective, except that nobody ever writes any of the orders down. T.T
There is a big difference at the cash register. Because food stamps can't be used for cooked food, the cooking fee must be charged separately as cash - which can get really complicated with the whole not writing anything down thing. But only to me, because everyone else there can do it in their heads. TT.TT