Unlike "5 Gb/s" USB, which in reality is 4 Gb/s USB, so a 5 Gb/s Ethernet interface cannot reach its maximum speed on a 5 Gb/s USB, the "10 Gb/s" USB is really 10 Gb/s, i.e. the difference between its real speed and 10 Gb/s is small enough to be negligible.

The same is true for 10 Gb/s Ethernet, whose speed is not exactly 10 Gb/s, but the difference from 10 Gb/s is also negligible.

Therefore, you do not need a 20 Gb/s USB to reach the maximum speed with a 10 Gb/s Ethernet interface, a 10 Gb/s USB port is good enough.

The overhead of data framing on USB is slightly higher than on Ethernet, so the maximum throughput on an USB 10 Gb/s Ethernet interface is a little lower than for a PCIe Ethernet NIC, but the difference is small enough to not matter. Usually other factors, like bad device drivers or inefficient programs, can cause much greater variations in Ethernet throughput.

The 9.4 Gb/s throughput obtained in TFA is perfectly reasonable when taking into account the packet overheads, which make impossible to reach 10 Gb/s for user data, regardless of hardware. A 20 Gb/s USB interface could not provide any serious improvement over that.