What you see here is 4 nodes that are using the messaging service, while the other nodes opted not to use it. The interesting part here is that the messaging chain and payment chain are connected so that when a message is sent from one user to the other there is a cost associated with it. That cost is reflected in the payment chain and saved on it, while the messaging chain saves the actual messages being sent out. What this means is users who opted not to use the messaging service dont have to keep files related to that service.
Every user (a node, in technical term) using ECC has the Payment Chain in their computers. You can think of a chain as a file that has all the transactions ever made in the network. Same way a bank has a history of all transactions that ever happened, so does every ECC user. The other chains (which end up being services) are optional and are built on top of this main chain.