How does OS X software update reboot works? Never used OS X before :(

This probably sounds stupid, sorry about that! but my OpenCore setup is my first OS X experience 😂

I just had my first build of OpenCore setup with High Sierra, still a WIP, and I saw a system update about 2.5GB in App Store. Hence, I went to install it.

After downloading, it runs for quite some time showing the apple boot screen with installing update text and then reboots. And here, I saw an additional boot option in OpenCore picker : Installer

I don't know whether I should choose Installer or my OSX boot disk, but I went ahead and choose Installer. Then it boots to a screen showing something like Installing MacOS, just like during first time setup, and it says about 45 minutes remaining.

Is this the correct step to let the updates install? Or I should actually boot to the OSX boot disk instead?