Even though you may not have installed Office you may have installed another application that used a part of Office in their product. Windows is seeing that you have something installed that needs an update.
The reason you are being asked to install a 32 bit version of the update is because you have a 32 bit version of Office installed. The default recommended version of Office to install from Microsoft is actually the 32 bit version. Just because you have a 64 bit computer does not mean that every application you run is also 64 bit. That is why you have the "C:\Program Files (x86)" folder on your computer. These are all of your 32 bit applications.
Basically, if Windows is suggesting to install a Microsoft security patch then you should install it. If you experience issues afterwards you can go back and uninstall patches.