The meaning of “nothing but” in English is closely related to the usage of “but” in all/anything/everything but, which is more idiomatic, however. “But” in the expression “nothing but” means “except”, i.e. “nothing but” is just a more emphatic way of saying “nothing except”, “only”; for example
We could see nothing but fog.
He causes nothing but trouble.
He causes nothing but trouble.
which means the same as
We could see nothing except fog.
He causes only trouble.
He causes only trouble.