One who's a non-resident of Canada for income tax purposes, and who's received income from a source within Canada, is generally subject to Canadian income tax on that income.
The Canadian tax rules for this are in Part XIII of the Income Tax Act. The terms "Part XIII tax", and "non-resident tax", are basically the same thing.
Canadians who make certain payments to non-residents are required to issue an NR4 tax slip to the non-resident for all such amounts paid during the year. For example, interest, dividends, and rental income are listed there. Employment income and business income aren't. (Over eighty different types of income requiring an NR4 slip are listed on the back of the slip.)
