Yes, I don't think there was ever any question that Tywin orchestrated the Red Wedding. The question was specifically about who's idea it was to sew Grey Wind's head onto Robb's body. No One (as in, the user, not literally no one) insinuated that it was Walder, while it strikes me as something that a crowd of soldiers might decide to do. We were wondering if it was ever specifically addressed.
edit: I swear No One's post was not there 5 minutes before I posted this. And by "swear" I mean that I almost certainly just overlooked it. Sorry