They are a public official in the sense that they work for a government office, but a city manager for a city of a million people is a job that is designed to operate "like the CEO of a business", as the article said. The kind of people qualified to take these positions are not common, and it is a highly compensated field when you are hiring for someone responsible for departments, etc. of such a large city. You are essentially hiring someone who could be running a mid to large size business.