Did he have residential ties to Canada during the period he earned it? Canada is not like the U.S., they tax on residency rather than citizenship; but there are all types of rules that factor into whether or not one is a resident of Canada in the eyes of Revenue Canada. Having a home with furniture it in Canada, even though one was physically present in the U.S. the entire year, is probably enough to make one a resident of Canada for income tax purposes.
You also have to report worldwide income if you want to apply for things like the GST credit, although that income that is not Canadian is not taxed.
