System Preferences Software Update

I recently upgraded from High Sierra to Mojave... This afternoon, I noticed that there is a "Software Update" tab in System Preferences. The Software Update tab indicates that there are two updates available to download and install...

For grins, I checked the App Store for updates (the mode I'm used to seeing notify me for updates), and it indicates that there are none available--all my apps are up to date.

Any thoughts as to this difference?

TIA

Bob