I agree with that last part but the people watching the athlete are definitely the customer. The athlete gets paid because people watch them on tv (and in person). If no one watched them on tv, then they quite literally would not get paid. Their employer is selling their talent and abilities (the product) to the watchers (the customers). The watchers are literally paying the athlete and the athletes employer, if not through subscriptions or tickets, then just by watching the ads on tv.