I guess the dollar goes a lot further in China? This isn't unheard of. Mexican illegals often do the same thing in this part of the country. They'll make decent money doing whatever -- lawn work, framing houses, roofing, etc. They'll send most of their check to Mexico where their families enjoy the good life.
Is the cost of living higher in Canada than the US? I know your income taxes (especially on the wealthy) are very high. From what I've found on this website, a typical citizen of Ontario who makes $113,804 or more pays a 40.6% provincial tax on their income plus 29% for their federal income tax (that's 69.6% of their income to the gov't) you also get to add other things like your Ontario medical premiums, etc. Add rent on top of that and I can see why folks do things like this:
http://www.taxtips.ca/tax_rates.htm#FederalTaxRates
Of course, these chinese students only have to pay 38.05% to income tax -- then they have to pay tuition (foriegners in the US have to pay higher tuition), they have to pay rent and for food which is pretty expensive in most college towns.
I can see how it'd be tough to make ends meet with a kid.