I have got this optional update some days ago for my laptop. I guess it's offered to all Windows 8.1 users. It's a driver update for the quite common usb to ethernet adapters based on an ASIX chip. In this case it's a chip used for the slow USB 2.0 to 100 Mb "Fast" Ethernet adapters.
MS released it on August 21st, so for them it's quite new. The origin driver from ASIX is probably from November 2013. I have no idea what took them so long to get it certified.
You probably won't need this driver for the SP3. I've got an ASIX based usb to ethernet adapter, but it's a fast USB 3.0 to Gigabit Ethernet adapter based on a newer ASIX chip. I wouldn't recommend a slow USB 2.0 to Fast Ethernet adapter for a SP3.