What I don't get is the definition of "volunteer" and have had many misleading definitions. For example, if a person helps out at a fundraiser, do they need a work permit? What about teaching a class at Holy Cross? What about helping at Saga a couple days a week? What about fundraising activities for Neighborhood Watch? Someone said that you don't need a work permit for non profit groups, but I am not so sure of that.
If you are not a resident or not holding work permit papers you technically need a volunteer permit for any of those activities. The stamp in your passport is pretty clear. The statement about not needing a permit for non profits is incorrect. What you were told at immigration is correct.