Simply removing NetUpdateFrequency fixes this problem
The 1 second update on the server is to simulate a poor network, if you remove it it will default to 100 which I guess is around 0.1 / 0.01 times a second or as fast as it can replicate on a local test environment. So if you are running the client and server on the same workstation it will appear to fix the issue. However in the real world where you would still see the jumping on a bad network.
You can test this by removing it as you have in your code, then not updating the code as this lecture but instead set the server to simulate lagging badly
the next few lectures are about how to better fake that interpolation where we have bad replication because of network so I would leave it at 1 sec for now so you can see the impact of the changes.