It is part of the fine print in the job contract for developers and is pretty common in most companies. You don't create a side project while being employed there without the company claiming ownership of it. It is part of a safety net for the companies so that they don't take a loss by an employee claiming copyright of code they wrote for the company during work hours.

According to law if there is no such clause the developer may claim ownership of code he wrote even if he was employed. The contract protects the company from that but also applies to any code written by employees generally (not a nice thing but prevalent).