The driver version you are referring to comes from the .INF files in the Arduino drivers folder.
Here is the relevant section from the .INF file that determines the version:
[Version]
Signature="$Windows NT$"
Class=Ports
ClassGuid={4D36E978-E325-11CE-BFC1-08002BE10318}
Provider=%MFGNAME%
LayoutFile=layout.inf
CatalogFile=%MFGFILENAME%.cat
DriverVer=11/15/2007,5.1.2600.0
This version is for informational purposes only and really has nothing to do with the actual Windows driver that does the work. The Windows driver that is used is USBSER.SYS . The .INF file simply instructs Windows to use the USBSER.SYS driver whenever the Arduino device is connected to the system.