The point is that you need to be well acquainted with the problem that you're trying to solve. If you're developing a new network protocol then yes, you don't need to know what kind of information is going to flow through the network, you need to know about network protocols. On the other hand, if you're developing a business application then you better know how that business works.
In the OPs specific example, the purpose of the network is to carry packets, and your job is to make sure packets are delivered. Whether they carry orders to launch nukes, or donations to charity isn't the purpose.