The guy in this video missed an important fact: he was using IPERF3 server on the WAN side, and client on the LAN side. Since IPERF3 by default send data from client to server, he is in fact testing upload. Client is always the sender by default. This can be reversed if the "-R" option is informed in the IPERF3 client command line.
This mistake does not fully invalidate the overall results, but nevertheless unless I missed something in the video the information he provided is not really accurate.
I've already purchased a NanoPI R4S, and when I receive it I will do a quick performance test with IPERF3 (similar to what I've done with the Redmi AX6S here).