Is a hop a jump between 2 switches/routers as opposed to a jump between a switch and a node? If its the latter then the diameter should be 8 right?

@kapalani Yes it seems that node switch links don't count.

Since for any network the node-switch links are necessary, it is not counted towards bandwidth.

Here nodes are acting as both endpoints and switches. Thus, we are not considering link between endpoint and switch towards diameter.