At first, he wasn't sure he wasn't dreaming. (Never create from your memory.) But he realized the feel of it was different, off somehow, before he realized why. It wasn't his memory, but Ariadne's. It was her intentions, her will, her desires and her memories.
Dom thought he understood why she had shot Mal in Limbo. (He had shot her on the mountain and it had hurt, so, so, so much. She might have been a dream, but she was your dream, you made her, you kept her alive, and she wasn't real.) But now he knew he did.
Was it closure? No. It was acceptance, or so he thought as he fell back against the mattress.