I have read this story several times. What Ziva did was not a mistake or a misunderstanding. What shows she did it with the intentions of hurting Tony because she knew it would and two, to give Gibbs the impression that Tony had refused her invite. As Abby pointed out, Ziva had sent out invitations.
What Gibbs did, he really deserved having Tony lay him out flat on his back. Just goes to show how little respect or caring he really has towards Tony. Gibbs had no right talking about Tony as he did behind his back. If Tony wanted Ziva to know he would have told her himself. But then, Gibbs has never really cared about Tony's feelings ever. Anything Tony has shared with Gibbs, Gibbs has been quick to share with Abby and Ducky. What Tony should have done was kick them both out of his apt and told Gibbs that he thought he could trust him for him to throw his trust back in his face