Edit 2: In short, it is grammatical because said is an adjective in this context, not a verb. This is the only grammatical interpretation of the phrase.
Consider if I were to write a paragraph and follow it with "That being verbose, you probably didn't read it all." I am describing the state of the paragraph which came before. It is verbose. Similarly, I can say that it is said, which is a phrase meaning "it has been said."
Edit: "Being said" in this context does not mean "being said right now." It means "being already said." "Said" is used as an adjective, not a verb. Consider the sentence "It's too late; the words are said."