Coaching is a process that aims to improve business performance and focuses on startup or existing businesses.
There are different coaching styles and levels of expertise. A business coach does not focus on expertise but focus on helping you learn how to use your skills to manage a successful business.
There is also a difference between teaching someone and helping them to learn. In coaching, of course the coach is helping the individual to improve their business performance but they are no doubt helping them to learn more about their business and how to better use their skills.