Nor do I, thought it could be justified as one of those "I told you what you needed to be told" kinds of well-meaning misdirections from his perspective. Although I think it's more likely he's speaking outright truthfully. Sylvanas likely knows anyone who was part of Thrall's old guard and circle of advisers is likely to be against her current plans in the same way Saurfang himself is, the same way Baine is. Thrall can very easily stir up dissent if he were roused - as he is here. And he goes on to help free Baine as well. In that sense, she's quite justified in her beliefs.