I feel like I'm stating the obvious here, but prices are set by a combination of both demand and supply. The article is focusing mostly on the demand side, but the supply factor makes a huge difference as well. There are significant immigrant populations from Mexico/China/India/Thailand, which means that someone opening a restaurant catering to these cuisines, can hire "ethnic chefs" at an affordable price.
In contrast, how big is the recently-French population in America really? And how many professional French cooks can one really find? Even if the demand for french food is much lower than the demand for Chinese food, the lack of supply alone will drive up the price.
Note also the second effect of the above. If someone wanted to open a Chinese restaurant, they can hire a affordable Chinese cook and market the restaurant as a mid-price restaurant. Or they can hire an expensive Chinese cook and market the restaurant as a high-end venue.
In contrast, if someone wanted to open a french restaurant, they don't have the option of hiring a cheap French cook. It's go big, or go home... which means that the pool of all French restaurants, is going to be heavily biased towards upscale, expensive restaurants.
If you simply take the average menu price of all zagat-rated French restaurants, and compare them to the average menu price of all zagat-rated Chinese restaurants, you're going to find a big difference in these average numbers, but a lot of it will simply be a result of the above price-bias. If you're trying to investigate people's demand/perception for a certain cuisine, the above results are going to be a highly distorted one.