Ha!
As I am located in Melbourne now, the times of nice 30 days/year paid vacation are gone for good.
Looks like there is a downside to everything.
Your assumptions are correct.
The network traffic in PlanViz gives you the inter-node data transfer during query execution.
Things like large joins of tables that are located on different nodes require data transfer between those nodes. And this this takes more time to perform the same operation in main memory on a single node, you will see longer execution times for such queries on multi-node systems.
This is one of the reasons for why on multi-node systems the data distribution is pretty important to get right. SAP BW on HANA does this mostly automatic (or is supposed to do it automatically - there are a few SAP notes with corrections for that out. So make sure these SAP notes are installed).
For the max memory metric, the SAP HANA revision you're using might be too old.
In any case, SPS 8 is now fairly ancient. SPS 11 is out and SPS 10 got it's maintenance revision. Time to upgrade!