I am willing to bet with at least 99% certainty that once you booted Windows after installing the card you got the message "Windows is searching for drivers for your new device" which would come right after the ballon pop up of "Windows has detected new hardware". As such the search had results for the adapter and installed them which allowed it to work without having to install drivers.
Oldskool is right, Windows is getting more and more advanced drivers included with the Os's now and as such there are default drivers for many devices out there.
My advice at this point would be to go to the Device Manager, check under the adapter's driver tab. Check the date listed for the driver and see if there is a newer driver out there. The driver, while it works, may be outdated and there could be a updated driver that fixes some known issues.