I think you may be thinking of the LD50 for rats. People have died from much less than 3g/kg.
The lethal dose was estimated to be less than 10 g of sodium (<5 teaspoons of salt) in two children, and less than 25 g sodium in four adults (<4 tablespoons of salt).
An acute toxicity from excess sodium intake with the possibility of fatal outcome has been reported in relation to the ingestion of huge amounts of sodium, such as 0.5–1 g of salt/kg body weight.
I think you may be thinking of the LD50 for rats. People have died from much less than 3g/kg.
https://pmc.ncbi.nlm.nih.gov/articles/PMC5537768/
https://pmc.ncbi.nlm.nih.gov/articles/PMC3951800/