You're right; however, under that rubric of committee business, and the fact that most issues that come before the committee in one way or another can be considered as committee business--such as asking the committee to consider a motion--Mr. Cullen's motion would fall under that rubric of committee business, allowing for the committee to consider it. In order to put a committee business item on, usually we would....
Mr. McGuinty provided the notice, and therefore it became an item for committee business. But since the committee is now on committee business and dealing with Mr. McGuinty's motion, then someone else, another member of the committee, can be recognized and, if they so wish, move another motion.
So that's essentially why. We could view it as perhaps a bit of a backdoor way to get future business or committee business onto the agenda.