On pages 1068 and 1069 of chapter 20 of O'Brien and Bosc, our rules and procedures, we talk about committees, and when we are talking about public servants appearing:
...public servants have been excused from commenting on the policy decisions made by the government. In addition, committees ordinarily accept the reasons that a public servant gives for declining to answer a specific question or series of questions which involve the giving of a legal opinion, which may be perceived as a conflict with the witness’ responsibility to the Minister...
Therefore Mr. Alexander is correct. I'll leave it to Colonel Gibson to answer as he sees fit.