Seaweed is a popular food for people to eat in particular in East Asia and South Africa:
So can chinchillas eat seaweed?
No, chinchillas cannot eat seaweed at all because it contains way too much salt.
If you were to feed a chinchilla seaweed it would make them sick because of the salt content.
Therefore please make sure you avoid this food and let your friends know as well who own a chinchilla.