I've never used HFSS so I don't know what does the re-normalized means.
However, from my point of view, there are some differences between matching and terminating port.
Matching mainly focuses on the port you are using, to make sure that you can get the maximum power transfer.
But terminating focuses on the unused port to cut that port off from the system you are testing.
In practical, the terminator are designed to absorb the incident power with little reflection so that it can not affect the measuring parameters.
Also, termination can make sure that the unused port will not resonate and not reflect the signal to damage a source and/or other devices.