Seth Roberts is right, and whoever is blogging for the Economist is wrong, as he (or she) would suspect if he lived under the broad blue skies of Alberta. The Chinese came to the Canadian West in great waves to build the CPR and other railroads in the late 19th century; for the most part they were, to say the least, neither expected nor encouraged to stay when the work was done. A few did, though, and as happened elsewhere, they often got into the restaurant trade. They didn't do so because a "concentration" of Chinese-Canadian population "created demand" for Chinese cuisine; if that had been so, there would have arisen just as many Ukrainian, German, Scottish, and Dutch restaurants. In fact, the Chinese food entrepreneurs tended to seek out new markets away from their original domiciles, such that every medium-sized town on the Canadian prairies, for most of the 20th century, possessed exactly one Chinese family whose business was running the local Chinese restaurant. I'm sure the tale has been much the same in other sparsely-settled frontier areas of the world.
The real factors that led to the ubiquity of Chinese food in Alberta and elsewhere are, pace Free Exchange, specific to the Chinese experience and the Chinese menu. As Roberts explains, Chinese restarauteurs were not seen to be taking away white men's jobs, and were thus in no danger of being chased out of town with a twelve-gauge in a time of otherwise profound anti-Chinese hostility. Cooking was a "safe" occupation, as were, in the same respect, laundering, gambling, and opium dealing. (Sorry: they're old-timey clichés for a reason.) Chinese cooking also lent itself, in ways other diaspora cuisines didn't, both to the use of low-priced varieties and cuts of meat and to the early adoption of a home-delivery model.
Some of the inherent market advantages of the Chinese chow-house are visible down to this day: they tend to remain open on major holidays, for instance, providing an attractive refuge for those who can't or won't cook and aren't being cooked for. And they continue to exert a mysterious magnetic influence on diaspora Jews—possibly a non-trivial factor in an uncivilized land with a few openly Jewish settlers and an enormous number of Eastern European emigrants whose names suddenly anglicized overnight in the steerage section of an ocean liner.