I'm betting it's because you made the latest Security update to
Mojave macOS 10.14. You can simply run the Terminal commands again to remove the "alert". but be prepared for the new warning:
Ignoring software updates is deprecated.
The ability to ignore individual updates will be removed in a future release of macOS.
I'm really, really getting tired of Apple's antics as regards OS updating...
Software Update changes in the latest macOS releases
