Back to the sea snails, my guess is they were put into a jar with little or no acidification. Low acid foods like seafood have to be pressure canned to inactivate Clostridium botulinum spores and the National Center for Home Food Preservation, the go-to source doesn’t have anything on snails.
Using the clam or oyster pressure canning processing times isn’t a good idea either – even those similar foods have different processing times due to heat penetration variability. Best to freeze the snails. Not sure about quality, but would avoid the botulism risks.