Not making minimum wage in the US? Come make less in China!
That being said, I do not personally find such teaching jobs enjoyable. And the author, it seems, is not well acquainted with the drawbacks (or advantages) of living in China. (Read Peter Hessler for an accurate account.)
I'd guess most teachers are probably pulling 15k USD per year between their main job and a couple of tutoring or corporate gigs on the side. It's better money than sitting in the basement, but it helps to keep things in perspective: a minimum wage job in California makes close to 24k these days and you can drink the milk.