Yes, it is. However, there is also a culture of offering treats to your co-workers. If your colleague insists on inviting you for a meal and paying for it, you can accept it to show friendliness. In return, you can also invite your co-workers for a meal and pay the bill. In Chinese culture, this kind of treating is regarded as a sort of reciprocal manner. It is an effective way of setting up friendships and relationships with others.